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      googlemock/docs/v1_5/CheatSheet.md
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# Defining a Mock Class #
## Mocking a Normal Class ##
Given
```
class Foo {
...
virtual ~Foo();
virtual int GetSize() const = 0;
virtual string Describe(const char* name) = 0;
virtual string Describe(int type) = 0;
virtual bool Process(Bar elem, int count) = 0;
};
```
(note that `~Foo()` **must** be virtual) we can define its mock as
```
#include <gmock/gmock.h>
class MockFoo : public Foo {
MOCK_CONST_METHOD0(GetSize, int());
MOCK_METHOD1(Describe, string(const char* name));
MOCK_METHOD1(Describe, string(int type));
MOCK_METHOD2(Process, bool(Bar elem, int count));
};
```
To create a "nice" mock object which ignores all uninteresting calls,
or a "strict" mock object, which treats them as failures:
```
NiceMock<MockFoo> nice_foo; // The type is a subclass of MockFoo.
StrictMock<MockFoo> strict_foo; // The type is a subclass of MockFoo.
```
## Mocking a Class Template ##
To mock
```
template <typename Elem>
class StackInterface {
public:
...
virtual ~StackInterface();
virtual int GetSize() const = 0;
virtual void Push(const Elem& x) = 0;
};
```
(note that `~StackInterface()` **must** be virtual) just append `_T` to the `MOCK_*` macros:
```
template <typename Elem>
class MockStack : public StackInterface<Elem> {
public:
...
MOCK_CONST_METHOD0_T(GetSize, int());
MOCK_METHOD1_T(Push, void(const Elem& x));
};
```
## Specifying Calling Conventions for Mock Functions ##
If your mock function doesn't use the default calling convention, you
can specify it by appending `_WITH_CALLTYPE` to any of the macros
described in the previous two sections and supplying the calling
convention as the first argument to the macro. For example,
```
MOCK_METHOD_1_WITH_CALLTYPE(STDMETHODCALLTYPE, Foo, bool(int n));
MOCK_CONST_METHOD2_WITH_CALLTYPE(STDMETHODCALLTYPE, Bar, int(double x, double y));
```
where `STDMETHODCALLTYPE` is defined by `<objbase.h>` on Windows.
# Using Mocks in Tests #
The typical flow is:
1. Import the Google Mock names you need to use. All Google Mock names are in the `testing` namespace unless they are macros or otherwise noted.
1. Create the mock objects.
1. Optionally, set the default actions of the mock objects.
1. Set your expectations on the mock objects (How will they be called? What wil they do?).
1. Exercise code that uses the mock objects; if necessary, check the result using [Google Test](http://code.google.com/p/googletest/) assertions.
1. When a mock objects is destructed, Google Mock automatically verifies that all expectations on it have been satisfied.
Here is an example:
```
using ::testing::Return; // #1
TEST(BarTest, DoesThis) {
MockFoo foo; // #2
ON_CALL(foo, GetSize()) // #3
.WillByDefault(Return(1));
// ... other default actions ...
EXPECT_CALL(foo, Describe(5)) // #4
.Times(3)
.WillRepeatedly(Return("Category 5"));
// ... other expectations ...
EXPECT_EQ("good", MyProductionFunction(&foo)); // #5
} // #6
```
# Setting Default Actions #
Google Mock has a **built-in default action** for any function that
returns `void`, `bool`, a numeric value, or a pointer.
To customize the default action for functions with return type `T` globally:
```
using ::testing::DefaultValue;
DefaultValue<T>::Set(value); // Sets the default value to be returned.
// ... use the mocks ...
DefaultValue<T>::Clear(); // Resets the default value.
```
To customize the default action for a particular method, use `ON_CALL()`:
```
ON_CALL(mock_object, method(matchers))
.With(multi_argument_matcher) ?
.WillByDefault(action);
```
# Setting Expectations #
`EXPECT_CALL()` sets **expectations** on a mock method (How will it be
called? What will it do?):
```
EXPECT_CALL(mock_object, method(matchers))
.With(multi_argument_matcher) ?
.Times(cardinality) ?
.InSequence(sequences) *
.After(expectations) *
.WillOnce(action) *
.WillRepeatedly(action) ?
.RetiresOnSaturation(); ?
```
If `Times()` is omitted, the cardinality is assumed to be:
* `Times(1)` when there is neither `WillOnce()` nor `WillRepeatedly()`;
* `Times(n)` when there are `n WillOnce()`s but no `WillRepeatedly()`, where `n` >= 1; or
* `Times(AtLeast(n))` when there are `n WillOnce()`s and a `WillRepeatedly()`, where `n` >= 0.
A method with no `EXPECT_CALL()` is free to be invoked _any number of times_, and the default action will be taken each time.
# Matchers #
A **matcher** matches a _single_ argument. You can use it inside
`ON_CALL()` or `EXPECT_CALL()`, or use it to validate a value
directly:
| `EXPECT_THAT(value, matcher)` | Asserts that `value` matches `matcher`. |
|:------------------------------|:----------------------------------------|
| `ASSERT_THAT(value, matcher)` | The same as `EXPECT_THAT(value, matcher)`, except that it generates a **fatal** failure. |
Built-in matchers (where `argument` is the function argument) are
divided into several categories:
## Wildcard ##
|`_`|`argument` can be any value of the correct type.|
|:--|:-----------------------------------------------|
|`A<type>()` or `An<type>()`|`argument` can be any value of type `type`. |
## Generic Comparison ##
|`Eq(value)` or `value`|`argument == value`|
|:---------------------|:------------------|
|`Ge(value)` |`argument >= value`|
|`Gt(value)` |`argument > value` |
|`Le(value)` |`argument <= value`|
|`Lt(value)` |`argument < value` |
|`Ne(value)` |`argument != value`|
|`IsNull()` |`argument` is a `NULL` pointer (raw or smart).|
|`NotNull()` |`argument` is a non-null pointer (raw or smart).|
|`Ref(variable)` |`argument` is a reference to `variable`.|
|`TypedEq<type>(value)`|`argument` has type `type` and is equal to `value`. You may need to use this instead of `Eq(value)` when the mock function is overloaded.|
Except `Ref()`, these matchers make a _copy_ of `value` in case it's
modified or destructed later. If the compiler complains that `value`
doesn't have a public copy constructor, try wrap it in `ByRef()`,
e.g. `Eq(ByRef(non_copyable_value))`. If you do that, make sure
`non_copyable_value` is not changed afterwards, or the meaning of your
matcher will be changed.
## Floating-Point Matchers ##
|`DoubleEq(a_double)`|`argument` is a `double` value approximately equal to `a_double`, treating two NaNs as unequal.|
|:-------------------|:----------------------------------------------------------------------------------------------|
|`FloatEq(a_float)` |`argument` is a `float` value approximately equal to `a_float`, treating two NaNs as unequal. |
|`NanSensitiveDoubleEq(a_double)`|`argument` is a `double` value approximately equal to `a_double`, treating two NaNs as equal. |
|`NanSensitiveFloatEq(a_float)`|`argument` is a `float` value approximately equal to `a_float`, treating two NaNs as equal. |
The above matchers use ULP-based comparison (the same as used in
[Google Test](http://code.google.com/p/googletest/)). They
automatically pick a reasonable error bound based on the absolute
value of the expected value. `DoubleEq()` and `FloatEq()` conform to
the IEEE standard, which requires comparing two NaNs for equality to
return false. The `NanSensitive*` version instead treats two NaNs as
equal, which is often what a user wants.
## String Matchers ##
The `argument` can be either a C string or a C++ string object:
|`ContainsRegex(string)`|`argument` matches the given regular expression.|
|:----------------------|:-----------------------------------------------|
|`EndsWith(suffix)` |`argument` ends with string `suffix`. |
|`HasSubstr(string)` |`argument` contains `string` as a sub-string. |
|`MatchesRegex(string)` |`argument` matches the given regular expression with the match starting at the first character and ending at the last character.|
|`StartsWith(prefix)` |`argument` starts with string `prefix`. |
|`StrCaseEq(string)` |`argument` is equal to `string`, ignoring case. |
|`StrCaseNe(string)` |`argument` is not equal to `string`, ignoring case.|
|`StrEq(string)` |`argument` is equal to `string`. |
|`StrNe(string)` |`argument` is not equal to `string`. |
`StrCaseEq()`, `StrCaseNe()`, `StrEq()`, and `StrNe()` work for wide
strings as well.
## Container Matchers ##
Most STL-style containers support `==`, so you can use
`Eq(expected_container)` or simply `expected_container` to match a
container exactly. If you want to write the elements in-line,
match them more flexibly, or get more informative messages, you can use:
| `Contains(e)` | `argument` contains an element that matches `e`, which can be either a value or a matcher. |
|:--------------|:-------------------------------------------------------------------------------------------|
|`ElementsAre(e0, e1, ..., en)`|`argument` has `n + 1` elements, where the i-th element matches `ei`, which can be a value or a matcher. 0 to 10 arguments are allowed.|
|`ElementsAreArray(array)` or `ElementsAreArray(array, count)`|The same as `ElementsAre()` except that the expected element values/matchers come from a C-style array.|
| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. |
These matchers can also match:
1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`), and
1. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer, int len)` -- see [Multi-argument Matchers](#Multiargument_Matchers.md)).
where the array may be multi-dimensional (i.e. its elements can be arrays).
## Member Matchers ##
|`Field(&class::field, m)`|`argument.field` (or `argument->field` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_.|
|:------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------|
|`Key(e)` |`argument.first` matches `e`, which can be either a value or a matcher. E.g. `Contains(Key(Le(5)))` can verify that a `map` contains a key `<= 5`.|
|`Pair(m1, m2)` |`argument` is an `std::pair` whose `first` field matches `m1` and `second` field matches `m2`. |
|`Property(&class::property, m)`|`argument.property()` (or `argument->property()` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_.|
## Matching the Result of a Function or Functor ##
|`ResultOf(f, m)`|`f(argument)` matches matcher `m`, where `f` is a function or functor.|
|:---------------|:---------------------------------------------------------------------|
## Pointer Matchers ##
|`Pointee(m)`|`argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`.|
|:-----------|:-----------------------------------------------------------------------------------------------|
## Multiargument Matchers ##
These are matchers on tuple types. They can be used in
`.With()`. The following can be used on functions with <i>two<br>
arguments</i> `x` and `y`:
|`Eq()`|`x == y`|
|:-----|:-------|
|`Ge()`|`x >= y`|
|`Gt()`|`x > y` |
|`Le()`|`x <= y`|
|`Lt()`|`x < y` |
|`Ne()`|`x != y`|
You can use the following selectors to pick a subset of the arguments
(or reorder them) to participate in the matching:
|`AllArgs(m)`|Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`.|
|:-----------|:-------------------------------------------------------------------|
|`Args<N1, N2, ..., Nk>(m)`|The `k` selected (using 0-based indices) arguments match `m`, e.g. `Args<1, 2>(Contains(5))`.|
## Composite Matchers ##
You can make a matcher from one or more other matchers:
|`AllOf(m1, m2, ..., mn)`|`argument` matches all of the matchers `m1` to `mn`.|
|:-----------------------|:---------------------------------------------------|
|`AnyOf(m1, m2, ..., mn)`|`argument` matches at least one of the matchers `m1` to `mn`.|
|`Not(m)` |`argument` doesn't match matcher `m`. |
## Adapters for Matchers ##
|`MatcherCast<T>(m)`|casts matcher `m` to type `Matcher<T>`.|
|:------------------|:--------------------------------------|
|`SafeMatcherCast<T>(m)`| [safely casts](V1_5_CookBook#Casting_Matchers.md) matcher `m` to type `Matcher<T>`. |
|`Truly(predicate)` |`predicate(argument)` returns something considered by C++ to be true, where `predicate` is a function or functor.|
## Matchers as Predicates ##
|`Matches(m)`|a unary functor that returns `true` if the argument matches `m`.|
|:-----------|:---------------------------------------------------------------|
|`ExplainMatchResult(m, value, result_listener)`|returns `true` if `value` matches `m`, explaining the result to `result_listener`.|
|`Value(x, m)`|returns `true` if the value of `x` matches `m`. |
## Defining Matchers ##
| `MATCHER(IsEven, "") { return (arg % 2) == 0; }` | Defines a matcher `IsEven()` to match an even number. |
|:-------------------------------------------------|:------------------------------------------------------|
| `MATCHER_P(IsDivisibleBy, n, "") { *result_listener << "where the remainder is " << (arg % n); return (arg % n) == 0; }` | Defines a macher `IsDivisibleBy(n)` to match a number divisible by `n`. |
| `MATCHER_P2(IsBetween, a, b, "is between %(a)s and %(b)s") { return a <= arg && arg <= b; }` | Defines a matcher `IsBetween(a, b)` to match a value in the range [`a`, `b`]. |
**Notes:**
1. The `MATCHER*` macros cannot be used inside a function or class.
1. The matcher body must be _purely functional_ (i.e. it cannot have any side effect, and the result must not depend on anything other than the value being matched and the matcher parameters).
1. You can use `PrintToString(x)` to convert a value `x` of any type to a string.
## Matchers as Test Assertions ##
|`ASSERT_THAT(expression, m)`|Generates a [fatal failure](http://code.google.com/p/googletest/wiki/GoogleTestPrimer#Assertions) if the value of `expression` doesn't match matcher `m`.|
|:---------------------------|:--------------------------------------------------------------------------------------------------------------------------------------------------------|
|`EXPECT_THAT(expression, m)`|Generates a non-fatal failure if the value of `expression` doesn't match matcher `m`. |
# Actions #
**Actions** specify what a mock function should do when invoked.
## Returning a Value ##
|`Return()`|Return from a `void` mock function.|
|:---------|:----------------------------------|
|`Return(value)`|Return `value`. |
|`ReturnArg<N>()`|Return the `N`-th (0-based) argument.|
|`ReturnNew<T>(a1, ..., ak)`|Return `new T(a1, ..., ak)`; a different object is created each time.|
|`ReturnNull()`|Return a null pointer. |
|`ReturnRef(variable)`|Return a reference to `variable`. |
## Side Effects ##
|`Assign(&variable, value)`|Assign `value` to variable.|
|:-------------------------|:--------------------------|
| `DeleteArg<N>()` | Delete the `N`-th (0-based) argument, which must be a pointer. |
| `SaveArg<N>(pointer)` | Save the `N`-th (0-based) argument to `*pointer`. |
| `SetArgReferee<N>(value)` | Assign value to the variable referenced by the `N`-th (0-based) argument. |
|`SetArgumentPointee<N>(value)`|Assign `value` to the variable pointed by the `N`-th (0-based) argument.|
|`SetArrayArgument<N>(first, last)`|Copies the elements in source range [`first`, `last`) to the array pointed to by the `N`-th (0-based) argument, which can be either a pointer or an iterator. The action does not take ownership of the elements in the source range.|
|`SetErrnoAndReturn(error, value)`|Set `errno` to `error` and return `value`.|
|`Throw(exception)` |Throws the given exception, which can be any copyable value. Available since v1.1.0.|
## Using a Function or a Functor as an Action ##
|`Invoke(f)`|Invoke `f` with the arguments passed to the mock function, where `f` can be a global/static function or a functor.|
|:----------|:-----------------------------------------------------------------------------------------------------------------|
|`Invoke(object_pointer, &class::method)`|Invoke the {method on the object with the arguments passed to the mock function. |
|`InvokeWithoutArgs(f)`|Invoke `f`, which can be a global/static function or a functor. `f` must take no arguments. |
|`InvokeWithoutArgs(object_pointer, &class::method)`|Invoke the method on the object, which takes no arguments. |
|`InvokeArgument<N>(arg1, arg2, ..., argk)`|Invoke the mock function's `N`-th (0-based) argument, which must be a function or a functor, with the `k` arguments.|
The return value of the invoked function is used as the return value
of the action.
When defining a function or functor to be used with `Invoke*()`, you can declare any unused parameters as `Unused`:
```
double Distance(Unused, double x, double y) { return sqrt(x*x + y*y); }
...
EXPECT_CALL(mock, Foo("Hi", _, _)).WillOnce(Invoke(Distance));
```
In `InvokeArgument<N>(...)`, if an argument needs to be passed by reference, wrap it inside `ByRef()`. For example,
```
InvokeArgument<2>(5, string("Hi"), ByRef(foo))
```
calls the mock function's #2 argument, passing to it `5` and `string("Hi")` by value, and `foo` by reference.
## Default Action ##
|`DoDefault()`|Do the default action (specified by `ON_CALL()` or the built-in one).|
|:------------|:--------------------------------------------------------------------|
**Note:** due to technical reasons, `DoDefault()` cannot be used inside a composite action - trying to do so will result in a run-time error.
## Composite Actions ##
|`DoAll(a1, a2, ..., an)`|Do all actions `a1` to `an` and return the result of `an` in each invocation. The first `n - 1` sub-actions must return void. |
|:-----------------------|:-----------------------------------------------------------------------------------------------------------------------------|
|`IgnoreResult(a)` |Perform action `a` and ignore its result. `a` must not return void. |
|`WithArg<N>(a)` |Pass the `N`-th (0-based) argument of the mock function to action `a` and perform it. |
|`WithArgs<N1, N2, ..., Nk>(a)`|Pass the selected (0-based) arguments of the mock function to action `a` and perform it. |
|`WithoutArgs(a)` |Perform action `a` without any arguments. |
## Defining Actions ##
| `ACTION(Sum) { return arg0 + arg1; }` | Defines an action `Sum()` to return the sum of the mock function's argument #0 and #1. |
|:--------------------------------------|:---------------------------------------------------------------------------------------|
| `ACTION_P(Plus, n) { return arg0 + n; }` | Defines an action `Plus(n)` to return the sum of the mock function's argument #0 and `n`. |
| `ACTION_Pk(Foo, p1, ..., pk) { statements; }` | Defines a parameterized action `Foo(p1, ..., pk)` to execute the given `statements`. |
The `ACTION*` macros cannot be used inside a function or class.
# Cardinalities #
These are used in `Times()` to specify how many times a mock function will be called:
|`AnyNumber()`|The function can be called any number of times.|
|:------------|:----------------------------------------------|
|`AtLeast(n)` |The call is expected at least `n` times. |
|`AtMost(n)` |The call is expected at most `n` times. |
|`Between(m, n)`|The call is expected between `m` and `n` (inclusive) times.|
|`Exactly(n) or n`|The call is expected exactly `n` times. In particular, the call should never happen when `n` is 0.|
# Expectation Order #
By default, the expectations can be matched in _any_ order. If some
or all expectations must be matched in a given order, there are two
ways to specify it. They can be used either independently or
together.
## The After Clause ##
```
using ::testing::Expectation;
...
Expectation init_x = EXPECT_CALL(foo, InitX());
Expectation init_y = EXPECT_CALL(foo, InitY());
EXPECT_CALL(foo, Bar())
.After(init_x, init_y);
```
says that `Bar()` can be called only after both `InitX()` and
`InitY()` have been called.
If you don't know how many pre-requisites an expectation has when you
write it, you can use an `ExpectationSet` to collect them:
```
using ::testing::ExpectationSet;
...
ExpectationSet all_inits;
for (int i = 0; i < element_count; i++) {
all_inits += EXPECT_CALL(foo, InitElement(i));
}
EXPECT_CALL(foo, Bar())
.After(all_inits);
```
says that `Bar()` can be called only after all elements have been
initialized (but we don't care about which elements get initialized
before the others).
Modifying an `ExpectationSet` after using it in an `.After()` doesn't
affect the meaning of the `.After()`.
## Sequences ##
When you have a long chain of sequential expectations, it's easier to
specify the order using **sequences**, which don't require you to given
each expectation in the chain a different name. <i>All expected<br>
calls</i> in the same sequence must occur in the order they are
specified.
```
using ::testing::Sequence;
Sequence s1, s2;
...
EXPECT_CALL(foo, Reset())
.InSequence(s1, s2)
.WillOnce(Return(true));
EXPECT_CALL(foo, GetSize())
.InSequence(s1)
.WillOnce(Return(1));
EXPECT_CALL(foo, Describe(A<const char*>()))
.InSequence(s2)
.WillOnce(Return("dummy"));
```
says that `Reset()` must be called before _both_ `GetSize()` _and_
`Describe()`, and the latter two can occur in any order.
To put many expectations in a sequence conveniently:
```
using ::testing::InSequence;
{
InSequence dummy;
EXPECT_CALL(...)...;
EXPECT_CALL(...)...;
...
EXPECT_CALL(...)...;
}
```
says that all expected calls in the scope of `dummy` must occur in
strict order. The name `dummy` is irrelevant.)
# Verifying and Resetting a Mock #
Google Mock will verify the expectations on a mock object when it is destructed, or you can do it earlier:
```
using ::testing::Mock;
...
// Verifies and removes the expectations on mock_obj;
// returns true iff successful.
Mock::VerifyAndClearExpectations(&mock_obj);
...
// Verifies and removes the expectations on mock_obj;
// also removes the default actions set by ON_CALL();
// returns true iff successful.
Mock::VerifyAndClear(&mock_obj);
```
You can also tell Google Mock that a mock object can be leaked and doesn't
need to be verified:
```
Mock::AllowLeak(&mock_obj);
```
# Mock Classes #
Google Mock defines a convenient mock class template
```
class MockFunction<R(A1, ..., An)> {
public:
MOCK_METHODn(Call, R(A1, ..., An));
};
```
See this [recipe](V1_5_CookBook#Using_Check_Points.md) for one application of it.
# Flags #
| `--gmock_catch_leaked_mocks=0` | Don't report leaked mock objects as failures. |
|:-------------------------------|:----------------------------------------------|
| `--gmock_verbose=LEVEL` | Sets the default verbosity level (`info`, `warning`, or `error`) of Google Mock messages. |

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This page lists all documentation wiki pages for Google Mock **version 1.5.0** -- **if you use a different version of Google Mock, please read the documentation for that specific version instead.**
* [ForDummies](V1_5_ForDummies.md) -- start here if you are new to Google Mock.
* [CheatSheet](V1_5_CheatSheet.md) -- a quick reference.
* [CookBook](V1_5_CookBook.md) -- recipes for doing various tasks using Google Mock.
* [FrequentlyAskedQuestions](V1_5_FrequentlyAskedQuestions.md) -- check here before asking a question on the mailing list.
To contribute code to Google Mock, read:
* DevGuide -- read this _before_ writing your first patch.
* [Pump Manual](http://code.google.com/p/googletest/wiki/PumpManual) -- how we generate some of Google Mock's source files.

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(**Note:** If you get compiler errors that you don't understand, be sure to consult [Google Mock Doctor](V1_5_FrequentlyAskedQuestions#How_am_I_supposed_to_make_sense_of_these_horrible_template_error.md).)
# What Is Google C++ Mocking Framework? #
When you write a prototype or test, often it's not feasible or wise to rely on real objects entirely. A **mock object** implements the same interface as a real object (so it can be used as one), but lets you specify at run time how it will be used and what it should do (which methods will be called? in which order? how many times? with what arguments? what will they return? etc).
**Note:** It is easy to confuse the term _fake objects_ with mock objects. Fakes and mocks actually mean very different things in the Test-Driven Development (TDD) community:
* **Fake** objects have working implementations, but usually take some shortcut (perhaps to make the operations less expensive), which makes them not suitable for production. An in-memory file system would be an example of a fake.
* **Mocks** are objects pre-programmed with _expectations_, which form a specification of the calls they are expected to receive.
If all this seems too abstract for you, don't worry - the most important thing to remember is that a mock allows you to check the _interaction_ between itself and code that uses it. The difference between fakes and mocks will become much clearer once you start to use mocks.
**Google C++ Mocking Framework** (or **Google Mock** for short) is a library (sometimes we also call it a "framework" to make it sound cool) for creating mock classes and using them. It does to C++ what [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/) do to Java.
Using Google Mock involves three basic steps:
1. Use some simple macros to describe the interface you want to mock, and they will expand to the implementation of your mock class;
1. Create some mock objects and specify its expectations and behavior using an intuitive syntax;
1. Exercise code that uses the mock objects. Google Mock will catch any violation of the expectations as soon as it arises.
# Why Google Mock? #
While mock objects help you remove unnecessary dependencies in tests and make them fast and reliable, using mocks manually in C++ is _hard_:
* Someone has to implement the mocks. The job is usually tedious and error-prone. No wonder people go great distance to avoid it.
* The quality of those manually written mocks is a bit, uh, unpredictable. You may see some really polished ones, but you may also see some that were hacked up in a hurry and have all sorts of ad hoc restrictions.
* The knowledge you gained from using one mock doesn't transfer to the next.
In contrast, Java and Python programmers have some fine mock frameworks, which automate the creation of mocks. As a result, mocking is a proven effective technique and widely adopted practice in those communities. Having the right tool absolutely makes the difference.
Google Mock was built to help C++ programmers. It was inspired by [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/), but designed with C++'s specifics in mind. It is your friend if any of the following problems is bothering you:
* You are stuck with a sub-optimal design and wish you had done more prototyping before it was too late, but prototyping in C++ is by no means "rapid".
* Your tests are slow as they depend on too many libraries or use expensive resources (e.g. a database).
* Your tests are brittle as some resources they use are unreliable (e.g. the network).
* You want to test how your code handles a failure (e.g. a file checksum error), but it's not easy to cause one.
* You need to make sure that your module interacts with other modules in the right way, but it's hard to observe the interaction; therefore you resort to observing the side effects at the end of the action, which is awkward at best.
* You want to "mock out" your dependencies, except that they don't have mock implementations yet; and, frankly, you aren't thrilled by some of those hand-written mocks.
We encourage you to use Google Mock as:
* a _design_ tool, for it lets you experiment with your interface design early and often. More iterations lead to better designs!
* a _testing_ tool to cut your tests' outbound dependencies and probe the interaction between your module and its collaborators.
# Getting Started #
Using Google Mock is easy! Inside your C++ source file, just `#include` `<gtest/gtest.h>` and `<gmock/gmock.h>`, and you are ready to go.
# A Case for Mock Turtles #
Let's look at an example. Suppose you are developing a graphics program that relies on a LOGO-like API for drawing. How would you test that it does the right thing? Well, you can run it and compare the screen with a golden screen snapshot, but let's admit it: tests like this are expensive to run and fragile (What if you just upgraded to a shiny new graphics card that has better anti-aliasing? Suddenly you have to update all your golden images.). It would be too painful if all your tests are like this. Fortunately, you learned about Dependency Injection and know the right thing to do: instead of having your application talk to the drawing API directly, wrap the API in an interface (say, `Turtle`) and code to that interface:
```
class Turtle {
...
virtual ~Turtle() {}
virtual void PenUp() = 0;
virtual void PenDown() = 0;
virtual void Forward(int distance) = 0;
virtual void Turn(int degrees) = 0;
virtual void GoTo(int x, int y) = 0;
virtual int GetX() const = 0;
virtual int GetY() const = 0;
};
```
(Note that the destructor of `Turtle` **must** be virtual, as is the case for **all** classes you intend to inherit from - otherwise the destructor of the derived class will not be called when you delete an object through a base pointer, and you'll get corrupted program states like memory leaks.)
You can control whether the turtle's movement will leave a trace using `PenUp()` and `PenDown()`, and control its movement using `Forward()`, `Turn()`, and `GoTo()`. Finally, `GetX()` and `GetY()` tell you the current position of the turtle.
Your program will normally use a real implementation of this interface. In tests, you can use a mock implementation instead. This allows you to easily check what drawing primitives your program is calling, with what arguments, and in which order. Tests written this way are much more robust (they won't break because your new machine does anti-aliasing differently), easier to read and maintain (the intent of a test is expressed in the code, not in some binary images), and run _much, much faster_.
# Writing the Mock Class #
If you are lucky, the mocks you need to use have already been implemented by some nice people. If, however, you find yourself in the position to write a mock class, relax - Google Mock turns this task into a fun game! (Well, almost.)
## How to Define It ##
Using the `Turtle` interface as example, here are the simple steps you need to follow:
1. Derive a class `MockTurtle` from `Turtle`.
1. Take a virtual function of `Turtle`. Count how many arguments it has.
1. In the `public:` section of the child class, write `MOCK_METHODn();` (or `MOCK_CONST_METHODn();` if you are mocking a `const` method), where `n` is the number of the arguments; if you counted wrong, shame on you, and a compiler error will tell you so.
1. Now comes the fun part: you take the function signature, cut-and-paste the _function name_ as the _first_ argument to the macro, and leave what's left as the _second_ argument (in case you're curious, this is the _type of the function_).
1. Repeat until all virtual functions you want to mock are done.
After the process, you should have something like:
```
#include <gmock/gmock.h> // Brings in Google Mock.
class MockTurtle : public Turtle {
public:
...
MOCK_METHOD0(PenUp, void());
MOCK_METHOD0(PenDown, void());
MOCK_METHOD1(Forward, void(int distance));
MOCK_METHOD1(Turn, void(int degrees));
MOCK_METHOD2(GoTo, void(int x, int y));
MOCK_CONST_METHOD0(GetX, int());
MOCK_CONST_METHOD0(GetY, int());
};
```
You don't need to define these mock methods somewhere else - the `MOCK_METHOD*` macros will generate the definitions for you. It's that simple! Once you get the hang of it, you can pump out mock classes faster than your source-control system can handle your check-ins.
**Tip:** If even this is too much work for you, you'll find the
`gmock_gen.py` tool in Google Mock's `scripts/generator/` directory (courtesy of the [cppclean](http://code.google.com/p/cppclean/) project) useful. This command-line
tool requires that you have Python 2.4 installed. You give it a C++ file and the name of an abstract class defined in it,
and it will print the definition of the mock class for you. Due to the
complexity of the C++ language, this script may not always work, but
it can be quite handy when it does. For more details, read the [user documentation](http://code.google.com/p/googlemock/source/browse/trunk/scripts/generator/README).
## Where to Put It ##
When you define a mock class, you need to decide where to put its definition. Some people put it in a `*_test.cc`. This is fine when the interface being mocked (say, `Foo`) is owned by the same person or team. Otherwise, when the owner of `Foo` changes it, your test could break. (You can't really expect `Foo`'s maintainer to fix every test that uses `Foo`, can you?)
So, the rule of thumb is: if you need to mock `Foo` and it's owned by others, define the mock class in `Foo`'s package (better, in a `testing` sub-package such that you can clearly separate production code and testing utilities), and put it in a `mock_foo.h`. Then everyone can reference `mock_foo.h` from their tests. If `Foo` ever changes, there is only one copy of `MockFoo` to change, and only tests that depend on the changed methods need to be fixed.
Another way to do it: you can introduce a thin layer `FooAdaptor` on top of `Foo` and code to this new interface. Since you own `FooAdaptor`, you can absorb changes in `Foo` much more easily. While this is more work initially, carefully choosing the adaptor interface can make your code easier to write and more readable (a net win in the long run), as you can choose `FooAdaptor` to fit your specific domain much better than `Foo` does.
# Using Mocks in Tests #
Once you have a mock class, using it is easy. The typical work flow is:
1. Import the Google Mock names from the `testing` namespace such that you can use them unqualified (You only have to do it once per file. Remember that namespaces are a good idea and good for your health.).
1. Create some mock objects.
1. Specify your expectations on them (How many times will a method be called? With what arguments? What should it do? etc.).
1. Exercise some code that uses the mocks; optionally, check the result using Google Test assertions. If a mock method is called more than expected or with wrong arguments, you'll get an error immediately.
1. When a mock is destructed, Google Mock will automatically check whether all expectations on it have been satisfied.
Here's an example:
```
#include "path/to/mock-turtle.h"
#include <gmock/gmock.h>
#include <gtest/gtest.h>
using ::testing::AtLeast; // #1
TEST(PainterTest, CanDrawSomething) {
MockTurtle turtle; // #2
EXPECT_CALL(turtle, PenDown()) // #3
.Times(AtLeast(1));
Painter painter(&turtle); // #4
EXPECT_TRUE(painter.DrawCircle(0, 0, 10));
} // #5
int main(int argc, char** argv) {
// The following line must be executed to initialize Google Mock
// (and Google Test) before running the tests.
::testing::InitGoogleMock(&argc, argv);
return RUN_ALL_TESTS();
}
```
As you might have guessed, this test checks that `PenDown()` is called at least once. If the `painter` object didn't call this method, your test will fail with a message like this:
```
path/to/my_test.cc:119: Failure
Actual function call count doesn't match this expectation:
Actually: never called;
Expected: called at least once.
```
**Tip 1:** If you run the test from an Emacs buffer, you can hit `<Enter>` on the line number displayed in the error message to jump right to the failed expectation.
**Tip 2:** If your mock objects are never deleted, the final verification won't happen. Therefore it's a good idea to use a heap leak checker in your tests when you allocate mocks on the heap.
**Important note:** Google Mock requires expectations to be set **before** the mock functions are called, otherwise the behavior is **undefined**. In particular, you mustn't interleave `EXPECT_CALL()`s and calls to the mock functions.
This means `EXPECT_CALL()` should be read as expecting that a call will occur _in the future_, not that a call has occurred. Why does Google Mock work like that? Well, specifying the expectation beforehand allows Google Mock to report a violation as soon as it arises, when the context (stack trace, etc) is still available. This makes debugging much easier.
Admittedly, this test is contrived and doesn't do much. You can easily achieve the same effect without using Google Mock. However, as we shall reveal soon, Google Mock allows you to do _much more_ with the mocks.
## Using Google Mock with Any Testing Framework ##
If you want to use something other than Google Test (e.g. [CppUnit](http://apps.sourceforge.net/mediawiki/cppunit/index.php?title=Main_Page) or
[CxxTest](http://cxxtest.tigris.org/)) as your testing framework, just change the `main()` function in the previous section to:
```
int main(int argc, char** argv) {
// The following line causes Google Mock to throw an exception on failure,
// which will be interpreted by your testing framework as a test failure.
::testing::GTEST_FLAG(throw_on_failure) = true;
::testing::InitGoogleMock(&argc, argv);
... whatever your testing framework requires ...
}
```
This approach has a catch: it makes Google Mock throw an exception
from a mock object's destructor sometimes. With some compilers, this
sometimes causes the test program to crash. You'll still be able to
notice that the test has failed, but it's not a graceful failure.
A better solution is to use Google Test's
[event listener API](http://code.google.com/p/googletest/wiki/GoogleTestAdvancedGuide#Extending_Google_Test_by_Handling_Test_Events)
to report a test failure to your testing framework properly. You'll need to
implement the `OnTestPartResult()` method of the event listener interface, but it
should be straightforward.
If this turns out to be too much work, we suggest that you stick with
Google Test, which works with Google Mock seamlessly (in fact, it is
technically part of Google Mock.). If there is a reason that you
cannot use Google Test, please let us know.
# Setting Expectations #
The key to using a mock object successfully is to set the _right expectations_ on it. If you set the expectations too strict, your test will fail as the result of unrelated changes. If you set them too loose, bugs can slip through. You want to do it just right such that your test can catch exactly the kind of bugs you intend it to catch. Google Mock provides the necessary means for you to do it "just right."
## General Syntax ##
In Google Mock we use the `EXPECT_CALL()` macro to set an expectation on a mock method. The general syntax is:
```
EXPECT_CALL(mock_object, method(matchers))
.Times(cardinality)
.WillOnce(action)
.WillRepeatedly(action);
```
The macro has two arguments: first the mock object, and then the method and its arguments. Note that the two are separated by a comma (`,`), not a period (`.`). (Why using a comma? The answer is that it was necessary for technical reasons.)
The macro can be followed by some optional _clauses_ that provide more information about the expectation. We'll discuss how each clause works in the coming sections.
This syntax is designed to make an expectation read like English. For example, you can probably guess that
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetX())
.Times(5)
.WillOnce(Return(100))
.WillOnce(Return(150))
.WillRepeatedly(Return(200));
```
says that the `turtle` object's `GetX()` method will be called five times, it will return 100 the first time, 150 the second time, and then 200 every time. Some people like to call this style of syntax a Domain-Specific Language (DSL).
**Note:** Why do we use a macro to do this? It serves two purposes: first it makes expectations easily identifiable (either by `grep` or by a human reader), and second it allows Google Mock to include the source file location of a failed expectation in messages, making debugging easier.
## Matchers: What Arguments Do We Expect? ##
When a mock function takes arguments, we must specify what arguments we are expecting; for example:
```
// Expects the turtle to move forward by 100 units.
EXPECT_CALL(turtle, Forward(100));
```
Sometimes you may not want to be too specific (Remember that talk about tests being too rigid? Over specification leads to brittle tests and obscures the intent of tests. Therefore we encourage you to specify only what's necessary - no more, no less.). If you care to check that `Forward()` will be called but aren't interested in its actual argument, write `_` as the argument, which means "anything goes":
```
using ::testing::_;
...
// Expects the turtle to move forward.
EXPECT_CALL(turtle, Forward(_));
```
`_` is an instance of what we call **matchers**. A matcher is like a predicate and can test whether an argument is what we'd expect. You can use a matcher inside `EXPECT_CALL()` wherever a function argument is expected.
A list of built-in matchers can be found in the [CheatSheet](V1_5_CheatSheet.md). For example, here's the `Ge` (greater than or equal) matcher:
```
using ::testing::Ge;...
EXPECT_CALL(turtle, Forward(Ge(100)));
```
This checks that the turtle will be told to go forward by at least 100 units.
## Cardinalities: How Many Times Will It Be Called? ##
The first clause we can specify following an `EXPECT_CALL()` is `Times()`. We call its argument a **cardinality** as it tells _how many times_ the call should occur. It allows us to repeat an expectation many times without actually writing it as many times. More importantly, a cardinality can be "fuzzy", just like a matcher can be. This allows a user to express the intent of a test exactly.
An interesting special case is when we say `Times(0)`. You may have guessed - it means that the function shouldn't be called with the given arguments at all, and Google Mock will report a Google Test failure whenever the function is (wrongfully) called.
We've seen `AtLeast(n)` as an example of fuzzy cardinalities earlier. For the list of built-in cardinalities you can use, see the [CheatSheet](V1_5_CheatSheet.md).
The `Times()` clause can be omitted. **If you omit `Times()`, Google Mock will infer the cardinality for you.** The rules are easy to remember:
* If **neither** `WillOnce()` **nor** `WillRepeatedly()` is in the `EXPECT_CALL()`, the inferred cardinality is `Times(1)`.
* If there are `n WillOnce()`'s but **no** `WillRepeatedly()`, where `n` >= 1, the cardinality is `Times(n)`.
* If there are `n WillOnce()`'s and **one** `WillRepeatedly()`, where `n` >= 0, the cardinality is `Times(AtLeast(n))`.
**Quick quiz:** what do you think will happen if a function is expected to be called twice but actually called four times?
## Actions: What Should It Do? ##
Remember that a mock object doesn't really have a working implementation? We as users have to tell it what to do when a method is invoked. This is easy in Google Mock.
First, if the return type of a mock function is a built-in type or a pointer, the function has a **default action** (a `void` function will just return, a `bool` function will return `false`, and other functions will return 0). If you don't say anything, this behavior will be used.
Second, if a mock function doesn't have a default action, or the default action doesn't suit you, you can specify the action to be taken each time the expectation matches using a series of `WillOnce()` clauses followed by an optional `WillRepeatedly()`. For example,
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillOnce(Return(300));
```
This says that `turtle.GetX()` will be called _exactly three times_ (Google Mock inferred this from how many `WillOnce()` clauses we've written, since we didn't explicitly write `Times()`), and will return 100, 200, and 300 respectively.
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetY())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillRepeatedly(Return(300));
```
says that `turtle.GetY()` will be called _at least twice_ (Google Mock knows this as we've written two `WillOnce()` clauses and a `WillRepeatedly()` while having no explicit `Times()`), will return 100 the first time, 200 the second time, and 300 from the third time on.
Of course, if you explicitly write a `Times()`, Google Mock will not try to infer the cardinality itself. What if the number you specified is larger than there are `WillOnce()` clauses? Well, after all `WillOnce()`s are used up, Google Mock will do the _default_ action for the function every time (unless, of course, you have a `WillRepeatedly()`.).
What can we do inside `WillOnce()` besides `Return()`? You can return a reference using `ReturnRef(variable)`, or invoke a pre-defined function, among [others](V1_5_CheatSheet#Actions.md).
**Important note:** The `EXPECT_CALL()` statement evaluates the action clause only once, even though the action may be performed many times. Therefore you must be careful about side effects. The following may not do what you want:
```
int n = 100;
EXPECT_CALL(turtle, GetX())
.Times(4)
.WillOnce(Return(n++));
```
Instead of returning 100, 101, 102, ..., consecutively, this mock function will always return 100 as `n++` is only evaluated once. Similarly, `Return(new Foo)` will create a new `Foo` object when the `EXPECT_CALL()` is executed, and will return the same pointer every time. If you want the side effect to happen every time, you need to define a custom action, which we'll teach in the [CookBook](V1_5_CookBook.md).
Time for another quiz! What do you think the following means?
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetY())
.Times(4)
.WillOnce(Return(100));
```
Obviously `turtle.GetY()` is expected to be called four times. But if you think it will return 100 every time, think twice! Remember that one `WillOnce()` clause will be consumed each time the function is invoked and the default action will be taken afterwards. So the right answer is that `turtle.GetY()` will return 100 the first time, but **return 0 from the second time on**, as returning 0 is the default action for `int` functions.
## Using Multiple Expectations ##
So far we've only shown examples where you have a single expectation. More realistically, you're going to specify expectations on multiple mock methods, which may be from multiple mock objects.
By default, when a mock method is invoked, Google Mock will search the expectations in the **reverse order** they are defined, and stop when an active expectation that matches the arguments is found (you can think of it as "newer rules override older ones."). If the matching expectation cannot take any more calls, you will get an upper-bound-violated failure. Here's an example:
```
using ::testing::_;...
EXPECT_CALL(turtle, Forward(_)); // #1
EXPECT_CALL(turtle, Forward(10)) // #2
.Times(2);
```
If `Forward(10)` is called three times in a row, the third time it will be an error, as the last matching expectation (#2) has been saturated. If, however, the third `Forward(10)` call is replaced by `Forward(20)`, then it would be OK, as now #1 will be the matching expectation.
**Side note:** Why does Google Mock search for a match in the _reverse_ order of the expectations? The reason is that this allows a user to set up the default expectations in a mock object's constructor or the test fixture's set-up phase and then customize the mock by writing more specific expectations in the test body. So, if you have two expectations on the same method, you want to put the one with more specific matchers **after** the other, or the more specific rule would be shadowed by the more general one that comes after it.
## Ordered vs Unordered Calls ##
By default, an expectation can match a call even though an earlier expectation hasn't been satisfied. In other words, the calls don't have to occur in the order the expectations are specified.
Sometimes, you may want all the expected calls to occur in a strict order. To say this in Google Mock is easy:
```
using ::testing::InSequence;...
TEST(FooTest, DrawsLineSegment) {
...
{
InSequence dummy;
EXPECT_CALL(turtle, PenDown());
EXPECT_CALL(turtle, Forward(100));
EXPECT_CALL(turtle, PenUp());
}
Foo();
}
```
By creating an object of type `InSequence`, all expectations in its scope are put into a _sequence_ and have to occur _sequentially_. Since we are just relying on the constructor and destructor of this object to do the actual work, its name is really irrelevant.
In this example, we test that `Foo()` calls the three expected functions in the order as written. If a call is made out-of-order, it will be an error.
(What if you care about the relative order of some of the calls, but not all of them? Can you specify an arbitrary partial order? The answer is ... yes! If you are impatient, the details can be found in the [CookBook](V1_5_CookBook.md).)
## All Expectations Are Sticky (Unless Said Otherwise) ##
Now let's do a quick quiz to see how well you can use this mock stuff already. How would you test that the turtle is asked to go to the origin _exactly twice_ (you want to ignore any other instructions it receives)?
After you've come up with your answer, take a look at ours and compare notes (solve it yourself first - don't cheat!):
```
using ::testing::_;...
EXPECT_CALL(turtle, GoTo(_, _)) // #1
.Times(AnyNumber());
EXPECT_CALL(turtle, GoTo(0, 0)) // #2
.Times(2);
```
Suppose `turtle.GoTo(0, 0)` is called three times. In the third time, Google Mock will see that the arguments match expectation #2 (remember that we always pick the last matching expectation). Now, since we said that there should be only two such calls, Google Mock will report an error immediately. This is basically what we've told you in the "Using Multiple Expectations" section above.
This example shows that **expectations in Google Mock are "sticky" by default**, in the sense that they remain active even after we have reached their invocation upper bounds. This is an important rule to remember, as it affects the meaning of the spec, and is **different** to how it's done in many other mocking frameworks (Why'd we do that? Because we think our rule makes the common cases easier to express and understand.).
Simple? Let's see if you've really understood it: what does the following code say?
```
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i));
}
```
If you think it says that `turtle.GetX()` will be called `n` times and will return 10, 20, 30, ..., consecutively, think twice! The problem is that, as we said, expectations are sticky. So, the second time `turtle.GetX()` is called, the last (latest) `EXPECT_CALL()` statement will match, and will immediately lead to an "upper bound exceeded" error - this piece of code is not very useful!
One correct way of saying that `turtle.GetX()` will return 10, 20, 30, ..., is to explicitly say that the expectations are _not_ sticky. In other words, they should _retire_ as soon as they are saturated:
```
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
```
And, there's a better way to do it: in this case, we expect the calls to occur in a specific order, and we line up the actions to match the order. Since the order is important here, we should make it explicit using a sequence:
```
using ::testing::InSequence;
using ::testing::Return;
...
{
InSequence s;
for (int i = 1; i <= n; i++) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
}
```
By the way, the other situation where an expectation may _not_ be sticky is when it's in a sequence - as soon as another expectation that comes after it in the sequence has been used, it automatically retires (and will never be used to match any call).
## Uninteresting Calls ##
A mock object may have many methods, and not all of them are that interesting. For example, in some tests we may not care about how many times `GetX()` and `GetY()` get called.
In Google Mock, if you are not interested in a method, just don't say anything about it. If a call to this method occurs, you'll see a warning in the test output, but it won't be a failure.
# What Now? #
Congratulations! You've learned enough about Google Mock to start using it. Now, you might want to join the [googlemock](http://groups.google.com/group/googlemock) discussion group and actually write some tests using Google Mock - it will be fun. Hey, it may even be addictive - you've been warned.
Then, if you feel like increasing your mock quotient, you should move on to the [CookBook](V1_5_CookBook.md). You can learn many advanced features of Google Mock there -- and advance your level of enjoyment and testing bliss.

624
googlemock/docs/v1_5/FrequentlyAskedQuestions.md
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@ -1,624 +0,0 @@
Please send your questions to the
[googlemock](http://groups.google.com/group/googlemock) discussion
group. If you need help with compiler errors, make sure you have
tried [Google Mock Doctor](#How_am_I_supposed_to_make_sense_of_these_horrible_template_error.md) first.
## I wrote some matchers. After I upgraded to a new version of Google Mock, they no longer compile. What's going on? ##
After version 1.4.0 of Google Mock was released, we had an idea on how
to make it easier to write matchers that can generate informative
messages efficiently. We experimented with this idea and liked what
we saw. Therefore we decided to implement it.
Unfortunately, this means that if you have defined your own matchers
by implementing `MatcherInterface` or using `MakePolymorphicMatcher()`,
your definitions will no longer compile. Matchers defined using the
`MATCHER*` family of macros are not affected.
Sorry for the hassle if your matchers are affected. We believe it's
in everyone's long-term interest to make this change sooner than
later. Fortunately, it's usually not hard to migrate an existing
matcher to the new API. Here's what you need to do:
If you wrote your matcher like this:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
you'll need to change it to:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
(i.e. rename `Matches()` to `MatchAndExplain()` and give it a second
argument of type `MatchResultListener*`.)
If you were also using `ExplainMatchResultTo()` to improve the matcher
message:
```
// Old matcher definition that doesn't work with the lastest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
virtual void ExplainMatchResultTo(MyType value,
::std::ostream* os) const {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Foo property is " << value.GetFoo();
}
...
};
```
you should move the logic of `ExplainMatchResultTo()` into
`MatchAndExplain()`, using the `MatchResultListener` argument where
the `::std::ostream` was used:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Foo property is " << value.GetFoo();
return value.GetFoo() > 5;
}
...
};
```
If your matcher is defined using `MakePolymorphicMatcher()`:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you should rename the `Matches()` method to `MatchAndExplain()` and
add a `MatchResultListener*` argument (the same as what you need to do
for matchers defined by implementing `MatcherInterface`):
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
If your polymorphic matcher uses `ExplainMatchResultTo()` for better
failure messages:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
void ExplainMatchResultTo(const MyGreatMatcher& matcher,
MyType value,
::std::ostream* os) {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Bar property is " << value.GetBar();
}
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you'll need to move the logic inside `ExplainMatchResultTo()` to
`MatchAndExplain()`:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Bar property is " << value.GetBar();
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
For more information, you can read these
[two](V1_5_CookBook#Writing_New_Monomorphic_Matchers.md)
[recipes](V1_5_CookBook#Writing_New_Polymorphic_Matchers.md)
from the cookbook. As always, you
are welcome to post questions on `googlemock@googlegroups.com` if you
need any help.
## When using Google Mock, do I have to use Google Test as the testing framework? I have my favorite testing framework and don't want to switch. ##
Google Mock works out of the box with Google Test. However, it's easy
to configure it to work with any testing framework of your choice.
[Here](V1_5_ForDummies#Using_Google_Mock_with_Any_Testing_Framework.md) is how.
## How am I supposed to make sense of these horrible template errors? ##
If you are confused by the compiler errors gcc threw at you,
try consulting the _Google Mock Doctor_ tool first. What it does is to
scan stdin for gcc error messages, and spit out diagnoses on the
problems (we call them diseases) your code has.
To "install", run command:
```
alias gmd='<path to googlemock>/scripts/gmock_doctor.py'
```
To use it, do:
```
<your-favorite-build-command> <your-test> 2>&1 | gmd
```
For example:
```
make my_test 2>&1 | gmd
```
Or you can run `gmd` and copy-n-paste gcc's error messages to it.
## Can I mock a variadic function? ##
You cannot mock a variadic function (i.e. a function taking ellipsis
(`...`) arguments) directly in Google Mock.
The problem is that in general, there is _no way_ for a mock object to
know how many arguments are passed to the variadic method, and what
the arguments' types are. Only the _author of the base class_ knows
the protocol, and we cannot look into his head.
Therefore, to mock such a function, the _user_ must teach the mock
object how to figure out the number of arguments and their types. One
way to do it is to provide overloaded versions of the function.
Ellipsis arguments are inherited from C and not really a C++ feature.
They are unsafe to use and don't work with arguments that have
constructors or destructors. Therefore we recommend to avoid them in
C++ as much as possible.
## MSVC gives me warning C4301 or C4373 when I define a mock method with a const parameter. Why? ##
If you compile this using Microsoft Visual C++ 2005 SP1:
```
class Foo {
...
virtual void Bar(const int i) = 0;
};
class MockFoo : public Foo {
...
MOCK_METHOD1(Bar, void(const int i));
};
```
You may get the following warning:
```
warning C4301: 'MockFoo::Bar': overriding virtual function only differs from 'Foo::Bar' by const/volatile qualifier
```
This is a MSVC bug. The same code compiles fine with gcc ,for
example. If you use Visual C++ 2008 SP1, you would get the warning:
```
warning C4373: 'MockFoo::Bar': virtual function overrides 'Foo::Bar', previous versions of the compiler did not override when parameters only differed by const/volatile qualifiers
```
In C++, if you _declare_ a function with a `const` parameter, the
`const` modifier is _ignored_. Therefore, the `Foo` base class above
is equivalent to:
```
class Foo {
...
virtual void Bar(int i) = 0; // int or const int? Makes no difference.
};
```
In fact, you can _declare_ Bar() with an `int` parameter, and _define_
it with a `const int` parameter. The compiler will still match them
up.
Since making a parameter `const` is meaningless in the method
_declaration_, we recommend to remove it in both `Foo` and `MockFoo`.
That should workaround the VC bug.
Note that we are talking about the _top-level_ `const` modifier here.
If the function parameter is passed by pointer or reference, declaring
the _pointee_ or _referee_ as `const` is still meaningful. For
example, the following two declarations are _not_ equivalent:
```
void Bar(int* p); // Neither p nor *p is const.
void Bar(const int* p); // p is not const, but *p is.
```
## I have a huge mock class, and Microsoft Visual C++ runs out of memory when compiling it. What can I do? ##
We've noticed that when the `/clr` compiler flag is used, Visual C++
uses 5~6 times as much memory when compiling a mock class. We suggest
to avoid `/clr` when compiling native C++ mocks.
## I can't figure out why Google Mock thinks my expectations are not satisfied. What should I do? ##
You might want to run your test with
`--gmock_verbose=info`. This flag lets Google Mock print a trace
of every mock function call it receives. By studying the trace,
you'll gain insights on why the expectations you set are not met.
## How can I assert that a function is NEVER called? ##
```
EXPECT_CALL(foo, Bar(_))
.Times(0);
```
## I have a failed test where Google Mock tells me TWICE that a particular expectation is not satisfied. Isn't this redundant? ##
When Google Mock detects a failure, it prints relevant information
(the mock function arguments, the state of relevant expectations, and
etc) to help the user debug. If another failure is detected, Google
Mock will do the same, including printing the state of relevant
expectations.
Sometimes an expectation's state didn't change between two failures,
and you'll see the same description of the state twice. They are
however _not_ redundant, as they refer to _different points in time_.
The fact they are the same _is_ interesting information.
## I get a heap check failure when using a mock object, but using a real object is fine. What can be wrong? ##
Does the class (hopefully a pure interface) you are mocking have a
virtual destructor?
Whenever you derive from a base class, make sure its destructor is
virtual. Otherwise Bad Things will happen. Consider the following
code:
```
class Base {
public:
// Not virtual, but should be.
~Base() { ... }
...
};
class Derived : public Base {
public:
...
private:
std::string value_;
};
...
Base* p = new Derived;
...
delete p; // Surprise! ~Base() will be called, but ~Derived() will not
// - value_ is leaked.
```
By changing `~Base()` to virtual, `~Derived()` will be correctly
called when `delete p` is executed, and the heap checker
will be happy.
## The "newer expectations override older ones" rule makes writing expectations awkward. Why does Google Mock do that? ##
When people complain about this, often they are referring to code like:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. However, I have to write the expectations in the
// reverse order. This sucks big time!!!
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
```
The problem is that they didn't pick the **best** way to express the test's
intent.
By default, expectations don't have to be matched in _any_ particular
order. If you want them to match in a certain order, you need to be
explicit. This is Google Mock's (and jMock's) fundamental philosophy: it's
easy to accidentally over-specify your tests, and we want to make it
harder to do so.
There are two better ways to write the test spec. You could either
put the expectations in sequence:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. Using a sequence, we can write the expectations
// in their natural order.
{
InSequence s;
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
}
```
or you can put the sequence of actions in the same expectation:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time.
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.WillOnce(Return(2))
.RetiresOnSaturation();
```
Back to the original questions: why does Google Mock search the
expectations (and `ON_CALL`s) from back to front? Because this
allows a user to set up a mock's behavior for the common case early
(e.g. in the mock's constructor or the test fixture's set-up phase)
and customize it with more specific rules later. If Google Mock
searches from front to back, this very useful pattern won't be
possible.
## Google Mock prints a warning when a function without EXPECT\_CALL is called, even if I have set its behavior using ON\_CALL. Would it be reasonable not to show the warning in this case? ##
When choosing between being neat and being safe, we lean toward the
latter. So the answer is that we think it's better to show the
warning.
Often people write `ON_CALL`s in the mock object's
constructor or `SetUp()`, as the default behavior rarely changes from
test to test. Then in the test body they set the expectations, which
are often different for each test. Having an `ON_CALL` in the set-up
part of a test doesn't mean that the calls are expected. If there's
no `EXPECT_CALL` and the method is called, it's possibly an error. If
we quietly let the call go through without notifying the user, bugs
may creep in unnoticed.
If, however, you are sure that the calls are OK, you can write
```
EXPECT_CALL(foo, Bar(_))
.WillRepeatedly(...);
```
instead of
```
ON_CALL(foo, Bar(_))
.WillByDefault(...);
```
This tells Google Mock that you do expect the calls and no warning should be
printed.
Also, you can control the verbosity using the `--gmock_verbose` flag.
If you find the output too noisy when debugging, just choose a less
verbose level.
## How can I delete the mock function's argument in an action? ##
If you find yourself needing to perform some action that's not
supported by Google Mock directly, remember that you can define your own
actions using
[MakeAction()](V1_5_CookBook#Writing_New_Actions.md) or
[MakePolymorphicAction()](V1_5_CookBook#Writing_New_Polymorphic_Actions.md),
or you can write a stub function and invoke it using
[Invoke()](V1_5_CookBook#Using_Functions_Methods_Functors.md).
## MOCK\_METHODn()'s second argument looks funny. Why don't you use the MOCK\_METHODn(Method, return\_type, arg\_1, ..., arg\_n) syntax? ##
What?! I think it's beautiful. :-)
While which syntax looks more natural is a subjective matter to some
extent, Google Mock's syntax was chosen for several practical advantages it
has.
Try to mock a function that takes a map as an argument:
```
virtual int GetSize(const map<int, std::string>& m);
```
Using the proposed syntax, it would be:
```
MOCK_METHOD1(GetSize, int, const map<int, std::string>& m);
```
Guess what? You'll get a compiler error as the compiler thinks that
`const map<int, std::string>& m` are **two**, not one, arguments. To work
around this you can use `typedef` to give the map type a name, but
that gets in the way of your work. Google Mock's syntax avoids this
problem as the function's argument types are protected inside a pair
of parentheses:
```
// This compiles fine.
MOCK_METHOD1(GetSize, int(const map<int, std::string>& m));
```
You still need a `typedef` if the return type contains an unprotected
comma, but that's much rarer.
Other advantages include:
1. `MOCK_METHOD1(Foo, int, bool)` can leave a reader wonder whether the method returns `int` or `bool`, while there won't be such confusion using Google Mock's syntax.
1. The way Google Mock describes a function type is nothing new, although many people may not be familiar with it. The same syntax was used in C, and the `function` library in `tr1` uses this syntax extensively. Since `tr1` will become a part of the new version of STL, we feel very comfortable to be consistent with it.
1. The function type syntax is also used in other parts of Google Mock's API (e.g. the action interface) in order to make the implementation tractable. A user needs to learn it anyway in order to utilize Google Mock's more advanced features. We'd as well stick to the same syntax in `MOCK_METHOD*`!
## My code calls a static/global function. Can I mock it? ##
You can, but you need to make some changes.
In general, if you find yourself needing to mock a static function,
it's a sign that your modules are too tightly coupled (and less
flexible, less reusable, less testable, etc). You are probably better
off defining a small interface and call the function through that
interface, which then can be easily mocked. It's a bit of work
initially, but usually pays for itself quickly.
This Google Testing Blog
[post](http://googletesting.blogspot.com/2008/06/defeat-static-cling.html)
says it excellently. Check it out.
## My mock object needs to do complex stuff. It's a lot of pain to specify the actions. Google Mock sucks! ##
I know it's not a question, but you get an answer for free any way. :-)
With Google Mock, you can create mocks in C++ easily. And people might be
tempted to use them everywhere. Sometimes they work great, and
sometimes you may find them, well, a pain to use. So, what's wrong in
the latter case?
When you write a test without using mocks, you exercise the code and
assert that it returns the correct value or that the system is in an
expected state. This is sometimes called "state-based testing".
Mocks are great for what some call "interaction-based" testing:
instead of checking the system state at the very end, mock objects
verify that they are invoked the right way and report an error as soon
as it arises, giving you a handle on the precise context in which the
error was triggered. This is often more effective and economical to
do than state-based testing.
If you are doing state-based testing and using a test double just to
simulate the real object, you are probably better off using a fake.
Using a mock in this case causes pain, as it's not a strong point for
mocks to perform complex actions. If you experience this and think
that mocks suck, you are just not using the right tool for your
problem. Or, you might be trying to solve the wrong problem. :-)
## I got a warning "Uninteresting function call encountered - default action taken.." Should I panic? ##
By all means, NO! It's just an FYI.
What it means is that you have a mock function, you haven't set any
expectations on it (by Google Mock's rule this means that you are not
interested in calls to this function and therefore it can be called
any number of times), and it is called. That's OK - you didn't say
it's not OK to call the function!
What if you actually meant to disallow this function to be called, but
forgot to write `EXPECT_CALL(foo, Bar()).Times(0)`? While
one can argue that it's the user's fault, Google Mock tries to be nice and
prints you a note.
So, when you see the message and believe that there shouldn't be any
uninteresting calls, you should investigate what's going on. To make
your life easier, Google Mock prints the function name and arguments
when an uninteresting call is encountered.
## I want to define a custom action. Should I use Invoke() or implement the action interface? ##
Either way is fine - you want to choose the one that's more convenient
for your circumstance.
Usually, if your action is for a particular function type, defining it
using `Invoke()` should be easier; if your action can be used in
functions of different types (e.g. if you are defining
`Return(value)`), `MakePolymorphicAction()` is
easiest. Sometimes you want precise control on what types of
functions the action can be used in, and implementing
`ActionInterface` is the way to go here. See the implementation of
`Return()` in `include/gmock/gmock-actions.h` for an example.
## I'm using the set-argument-pointee action, and the compiler complains about "conflicting return type specified". What does it mean? ##
You got this error as Google Mock has no idea what value it should return
when the mock method is called. `SetArgumentPointee()` says what the
side effect is, but doesn't say what the return value should be. You
need `DoAll()` to chain a `SetArgumentPointee()` with a `Return()`.
See this [recipe](V1_5_CookBook#Mocking_Side_Effects.md) for more details and an example.
## My question is not in your FAQ! ##
If you cannot find the answer to your question in this FAQ, there are
some other resources you can use:
1. read other [wiki pages](http://code.google.com/p/googlemock/w/list),
1. search the mailing list [archive](http://groups.google.com/group/googlemock/topics),
1. ask it on [googlemock@googlegroups.com](mailto:googlemock@googlegroups.com) and someone will answer it (to prevent spam, we require you to join the [discussion group](http://groups.google.com/group/googlemock) before you can post.).
Please note that creating an issue in the
[issue tracker](http://code.google.com/p/googlemock/issues/list) is _not_
a good way to get your answer, as it is monitored infrequently by a
very small number of people.
When asking a question, it's helpful to provide as much of the
following information as possible (people cannot help you if there's
not enough information in your question):
* the version (or the revision number if you check out from SVN directly) of Google Mock you use (Google Mock is under active development, so it's possible that your problem has been solved in a later version),
* your operating system,
* the name and version of your compiler,
* the complete command line flags you give to your compiler,
* the complete compiler error messages (if the question is about compilation),
* the _actual_ code (ideally, a minimal but complete program) that has the problem you encounter.

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# Defining a Mock Class #
## Mocking a Normal Class ##
Given
```
class Foo {
...
virtual ~Foo();
virtual int GetSize() const = 0;
virtual string Describe(const char* name) = 0;
virtual string Describe(int type) = 0;
virtual bool Process(Bar elem, int count) = 0;
};
```
(note that `~Foo()` **must** be virtual) we can define its mock as
```
#include "gmock/gmock.h"
class MockFoo : public Foo {
MOCK_CONST_METHOD0(GetSize, int());
MOCK_METHOD1(Describe, string(const char* name));
MOCK_METHOD1(Describe, string(int type));
MOCK_METHOD2(Process, bool(Bar elem, int count));
};
```
To create a "nice" mock object which ignores all uninteresting calls,
or a "strict" mock object, which treats them as failures:
```
NiceMock<MockFoo> nice_foo; // The type is a subclass of MockFoo.
StrictMock<MockFoo> strict_foo; // The type is a subclass of MockFoo.
```
## Mocking a Class Template ##
To mock
```
template <typename Elem>
class StackInterface {
public:
...
virtual ~StackInterface();
virtual int GetSize() const = 0;
virtual void Push(const Elem& x) = 0;
};
```
(note that `~StackInterface()` **must** be virtual) just append `_T` to the `MOCK_*` macros:
```
template <typename Elem>
class MockStack : public StackInterface<Elem> {
public:
...
MOCK_CONST_METHOD0_T(GetSize, int());
MOCK_METHOD1_T(Push, void(const Elem& x));
};
```
## Specifying Calling Conventions for Mock Functions ##
If your mock function doesn't use the default calling convention, you
can specify it by appending `_WITH_CALLTYPE` to any of the macros
described in the previous two sections and supplying the calling
convention as the first argument to the macro. For example,
```
MOCK_METHOD_1_WITH_CALLTYPE(STDMETHODCALLTYPE, Foo, bool(int n));
MOCK_CONST_METHOD2_WITH_CALLTYPE(STDMETHODCALLTYPE, Bar, int(double x, double y));
```
where `STDMETHODCALLTYPE` is defined by `<objbase.h>` on Windows.
# Using Mocks in Tests #
The typical flow is:
1. Import the Google Mock names you need to use. All Google Mock names are in the `testing` namespace unless they are macros or otherwise noted.
1. Create the mock objects.
1. Optionally, set the default actions of the mock objects.
1. Set your expectations on the mock objects (How will they be called? What wil they do?).
1. Exercise code that uses the mock objects; if necessary, check the result using [Google Test](http://code.google.com/p/googletest/) assertions.
1. When a mock objects is destructed, Google Mock automatically verifies that all expectations on it have been satisfied.
Here is an example:
```
using ::testing::Return; // #1
TEST(BarTest, DoesThis) {
MockFoo foo; // #2
ON_CALL(foo, GetSize()) // #3
.WillByDefault(Return(1));
// ... other default actions ...
EXPECT_CALL(foo, Describe(5)) // #4
.Times(3)
.WillRepeatedly(Return("Category 5"));
// ... other expectations ...
EXPECT_EQ("good", MyProductionFunction(&foo)); // #5
} // #6
```
# Setting Default Actions #
Google Mock has a **built-in default action** for any function that
returns `void`, `bool`, a numeric value, or a pointer.
To customize the default action for functions with return type `T` globally:
```
using ::testing::DefaultValue;
DefaultValue<T>::Set(value); // Sets the default value to be returned.
// ... use the mocks ...
DefaultValue<T>::Clear(); // Resets the default value.
```
To customize the default action for a particular method, use `ON_CALL()`:
```
ON_CALL(mock_object, method(matchers))
.With(multi_argument_matcher) ?
.WillByDefault(action);
```
# Setting Expectations #
`EXPECT_CALL()` sets **expectations** on a mock method (How will it be
called? What will it do?):
```
EXPECT_CALL(mock_object, method(matchers))
.With(multi_argument_matcher) ?
.Times(cardinality) ?
.InSequence(sequences) *
.After(expectations) *
.WillOnce(action) *
.WillRepeatedly(action) ?
.RetiresOnSaturation(); ?
```
If `Times()` is omitted, the cardinality is assumed to be:
* `Times(1)` when there is neither `WillOnce()` nor `WillRepeatedly()`;
* `Times(n)` when there are `n WillOnce()`s but no `WillRepeatedly()`, where `n` >= 1; or
* `Times(AtLeast(n))` when there are `n WillOnce()`s and a `WillRepeatedly()`, where `n` >= 0.
A method with no `EXPECT_CALL()` is free to be invoked _any number of times_, and the default action will be taken each time.
# Matchers #
A **matcher** matches a _single_ argument. You can use it inside
`ON_CALL()` or `EXPECT_CALL()`, or use it to validate a value
directly:
| `EXPECT_THAT(value, matcher)` | Asserts that `value` matches `matcher`. |
|:------------------------------|:----------------------------------------|
| `ASSERT_THAT(value, matcher)` | The same as `EXPECT_THAT(value, matcher)`, except that it generates a **fatal** failure. |
Built-in matchers (where `argument` is the function argument) are
divided into several categories:
## Wildcard ##
|`_`|`argument` can be any value of the correct type.|
|:--|:-----------------------------------------------|
|`A<type>()` or `An<type>()`|`argument` can be any value of type `type`. |
## Generic Comparison ##
|`Eq(value)` or `value`|`argument == value`|
|:---------------------|:------------------|
|`Ge(value)` |`argument >= value`|
|`Gt(value)` |`argument > value` |
|`Le(value)` |`argument <= value`|
|`Lt(value)` |`argument < value` |
|`Ne(value)` |`argument != value`|
|`IsNull()` |`argument` is a `NULL` pointer (raw or smart).|
|`NotNull()` |`argument` is a non-null pointer (raw or smart).|
|`Ref(variable)` |`argument` is a reference to `variable`.|
|`TypedEq<type>(value)`|`argument` has type `type` and is equal to `value`. You may need to use this instead of `Eq(value)` when the mock function is overloaded.|
Except `Ref()`, these matchers make a _copy_ of `value` in case it's
modified or destructed later. If the compiler complains that `value`
doesn't have a public copy constructor, try wrap it in `ByRef()`,
e.g. `Eq(ByRef(non_copyable_value))`. If you do that, make sure
`non_copyable_value` is not changed afterwards, or the meaning of your
matcher will be changed.
## Floating-Point Matchers ##
|`DoubleEq(a_double)`|`argument` is a `double` value approximately equal to `a_double`, treating two NaNs as unequal.|
|:-------------------|:----------------------------------------------------------------------------------------------|
|`FloatEq(a_float)` |`argument` is a `float` value approximately equal to `a_float`, treating two NaNs as unequal. |
|`NanSensitiveDoubleEq(a_double)`|`argument` is a `double` value approximately equal to `a_double`, treating two NaNs as equal. |
|`NanSensitiveFloatEq(a_float)`|`argument` is a `float` value approximately equal to `a_float`, treating two NaNs as equal. |
These matchers use ULP-based comparison (the same as used in
[Google Test](http://code.google.com/p/googletest/)). They
automatically pick a reasonable error bound based on the absolute
value of the expected value. `DoubleEq()` and `FloatEq()` conform to
the IEEE standard, which requires comparing two NaNs for equality to
return false. The `NanSensitive*` version instead treats two NaNs as
equal, which is often what a user wants.
## String Matchers ##
The `argument` can be either a C string or a C++ string object:
|`ContainsRegex(string)`|`argument` matches the given regular expression.|
|:----------------------|:-----------------------------------------------|
|`EndsWith(suffix)` |`argument` ends with string `suffix`. |
|`HasSubstr(string)` |`argument` contains `string` as a sub-string. |
|`MatchesRegex(string)` |`argument` matches the given regular expression with the match starting at the first character and ending at the last character.|
|`StartsWith(prefix)` |`argument` starts with string `prefix`. |
|`StrCaseEq(string)` |`argument` is equal to `string`, ignoring case. |
|`StrCaseNe(string)` |`argument` is not equal to `string`, ignoring case.|
|`StrEq(string)` |`argument` is equal to `string`. |
|`StrNe(string)` |`argument` is not equal to `string`. |
`ContainsRegex()` and `MatchesRegex()` use the regular expression
syntax defined
[here](http://code.google.com/p/googletest/wiki/V1_6_AdvancedGuide#Regular_Expression_Syntax).
`StrCaseEq()`, `StrCaseNe()`, `StrEq()`, and `StrNe()` work for wide
strings as well.
## Container Matchers ##
Most STL-style containers support `==`, so you can use
`Eq(expected_container)` or simply `expected_container` to match a
container exactly. If you want to write the elements in-line,
match them more flexibly, or get more informative messages, you can use:
| `Contains(e)` | `argument` contains an element that matches `e`, which can be either a value or a matcher. |
|:--------------|:-------------------------------------------------------------------------------------------|
| `Each(e)` | `argument` is a container where _every_ element matches `e`, which can be either a value or a matcher. |
| `ElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, where the i-th element matches `ei`, which can be a value or a matcher. 0 to 10 arguments are allowed. |
| `ElementsAreArray(array)` or `ElementsAreArray(array, count)` | The same as `ElementsAre()` except that the expected element values/matchers come from a C-style array. |
| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. |
| `Pointwise(m, container)` | `argument` contains the same number of elements as in `container`, and for all i, (the i-th element in `argument`, the i-th element in `container`) match `m`, which is a matcher on 2-tuples. E.g. `Pointwise(Le(), upper_bounds)` verifies that each element in `argument` doesn't exceed the corresponding element in `upper_bounds`. |
These matchers can also match:
1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`), and
1. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer, int len)` -- see [Multi-argument Matchers](#Multiargument_Matchers.md)).
where the array may be multi-dimensional (i.e. its elements can be arrays).
## Member Matchers ##
|`Field(&class::field, m)`|`argument.field` (or `argument->field` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_.|
|:------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------|
|`Key(e)` |`argument.first` matches `e`, which can be either a value or a matcher. E.g. `Contains(Key(Le(5)))` can verify that a `map` contains a key `<= 5`.|
|`Pair(m1, m2)` |`argument` is an `std::pair` whose `first` field matches `m1` and `second` field matches `m2`. |
|`Property(&class::property, m)`|`argument.property()` (or `argument->property()` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_.|
## Matching the Result of a Function or Functor ##
|`ResultOf(f, m)`|`f(argument)` matches matcher `m`, where `f` is a function or functor.|
|:---------------|:---------------------------------------------------------------------|
## Pointer Matchers ##
|`Pointee(m)`|`argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`.|
|:-----------|:-----------------------------------------------------------------------------------------------|
## Multiargument Matchers ##
Technically, all matchers match a _single_ value. A "multi-argument"
matcher is just one that matches a _tuple_. The following matchers can
be used to match a tuple `(x, y)`:
|`Eq()`|`x == y`|
|:-----|:-------|
|`Ge()`|`x >= y`|
|`Gt()`|`x > y` |
|`Le()`|`x <= y`|
|`Lt()`|`x < y` |
|`Ne()`|`x != y`|
You can use the following selectors to pick a subset of the arguments
(or reorder them) to participate in the matching:
|`AllArgs(m)`|Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`.|
|:-----------|:-------------------------------------------------------------------|
|`Args<N1, N2, ..., Nk>(m)`|The tuple of the `k` selected (using 0-based indices) arguments matches `m`, e.g. `Args<1, 2>(Eq())`.|
## Composite Matchers ##
You can make a matcher from one or more other matchers:
|`AllOf(m1, m2, ..., mn)`|`argument` matches all of the matchers `m1` to `mn`.|
|:-----------------------|:---------------------------------------------------|
|`AnyOf(m1, m2, ..., mn)`|`argument` matches at least one of the matchers `m1` to `mn`.|
|`Not(m)` |`argument` doesn't match matcher `m`. |
## Adapters for Matchers ##
|`MatcherCast<T>(m)`|casts matcher `m` to type `Matcher<T>`.|
|:------------------|:--------------------------------------|
|`SafeMatcherCast<T>(m)`| [safely casts](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Casting_Matchers) matcher `m` to type `Matcher<T>`. |
|`Truly(predicate)` |`predicate(argument)` returns something considered by C++ to be true, where `predicate` is a function or functor.|
## Matchers as Predicates ##
|`Matches(m)(value)`|evaluates to `true` if `value` matches `m`. You can use `Matches(m)` alone as a unary functor.|
|:------------------|:---------------------------------------------------------------------------------------------|
|`ExplainMatchResult(m, value, result_listener)`|evaluates to `true` if `value` matches `m`, explaining the result to `result_listener`. |
|`Value(value, m)` |evaluates to `true` if `value` matches `m`. |
## Defining Matchers ##
| `MATCHER(IsEven, "") { return (arg % 2) == 0; }` | Defines a matcher `IsEven()` to match an even number. |
|:-------------------------------------------------|:------------------------------------------------------|
| `MATCHER_P(IsDivisibleBy, n, "") { *result_listener << "where the remainder is " << (arg % n); return (arg % n) == 0; }` | Defines a macher `IsDivisibleBy(n)` to match a number divisible by `n`. |
| `MATCHER_P2(IsBetween, a, b, std::string(negation ? "isn't" : "is") + " between " + PrintToString(a) + " and " + PrintToString(b)) { return a <= arg && arg <= b; }` | Defines a matcher `IsBetween(a, b)` to match a value in the range [`a`, `b`]. |
**Notes:**
1. The `MATCHER*` macros cannot be used inside a function or class.
1. The matcher body must be _purely functional_ (i.e. it cannot have any side effect, and the result must not depend on anything other than the value being matched and the matcher parameters).
1. You can use `PrintToString(x)` to convert a value `x` of any type to a string.
## Matchers as Test Assertions ##
|`ASSERT_THAT(expression, m)`|Generates a [fatal failure](http://code.google.com/p/googletest/wiki/V1_6_Primer#Assertions) if the value of `expression` doesn't match matcher `m`.|
|:---------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------|
|`EXPECT_THAT(expression, m)`|Generates a non-fatal failure if the value of `expression` doesn't match matcher `m`. |
# Actions #
**Actions** specify what a mock function should do when invoked.
## Returning a Value ##
|`Return()`|Return from a `void` mock function.|
|:---------|:----------------------------------|
|`Return(value)`|Return `value`. If the type of `value` is different to the mock function's return type, `value` is converted to the latter type <i>at the time the expectation is set</i>, not when the action is executed.|
|`ReturnArg<N>()`|Return the `N`-th (0-based) argument.|
|`ReturnNew<T>(a1, ..., ak)`|Return `new T(a1, ..., ak)`; a different object is created each time.|
|`ReturnNull()`|Return a null pointer. |
|`ReturnPointee(ptr)`|Return the value pointed to by `ptr`.|
|`ReturnRef(variable)`|Return a reference to `variable`. |
|`ReturnRefOfCopy(value)`|Return a reference to a copy of `value`; the copy lives as long as the action.|
## Side Effects ##
|`Assign(&variable, value)`|Assign `value` to variable.|
|:-------------------------|:--------------------------|
| `DeleteArg<N>()` | Delete the `N`-th (0-based) argument, which must be a pointer. |
| `SaveArg<N>(pointer)` | Save the `N`-th (0-based) argument to `*pointer`. |
| `SaveArgPointee<N>(pointer)` | Save the value pointed to by the `N`-th (0-based) argument to `*pointer`. |
| `SetArgReferee<N>(value)` | Assign value to the variable referenced by the `N`-th (0-based) argument. |
|`SetArgPointee<N>(value)` |Assign `value` to the variable pointed by the `N`-th (0-based) argument.|
|`SetArgumentPointee<N>(value)`|Same as `SetArgPointee<N>(value)`. Deprecated. Will be removed in v1.7.0.|
|`SetArrayArgument<N>(first, last)`|Copies the elements in source range [`first`, `last`) to the array pointed to by the `N`-th (0-based) argument, which can be either a pointer or an iterator. The action does not take ownership of the elements in the source range.|
|`SetErrnoAndReturn(error, value)`|Set `errno` to `error` and return `value`.|
|`Throw(exception)` |Throws the given exception, which can be any copyable value. Available since v1.1.0.|
## Using a Function or a Functor as an Action ##
|`Invoke(f)`|Invoke `f` with the arguments passed to the mock function, where `f` can be a global/static function or a functor.|
|:----------|:-----------------------------------------------------------------------------------------------------------------|
|`Invoke(object_pointer, &class::method)`|Invoke the {method on the object with the arguments passed to the mock function. |
|`InvokeWithoutArgs(f)`|Invoke `f`, which can be a global/static function or a functor. `f` must take no arguments. |
|`InvokeWithoutArgs(object_pointer, &class::method)`|Invoke the method on the object, which takes no arguments. |
|`InvokeArgument<N>(arg1, arg2, ..., argk)`|Invoke the mock function's `N`-th (0-based) argument, which must be a function or a functor, with the `k` arguments.|
The return value of the invoked function is used as the return value
of the action.
When defining a function or functor to be used with `Invoke*()`, you can declare any unused parameters as `Unused`:
```
double Distance(Unused, double x, double y) { return sqrt(x*x + y*y); }
...
EXPECT_CALL(mock, Foo("Hi", _, _)).WillOnce(Invoke(Distance));
```
In `InvokeArgument<N>(...)`, if an argument needs to be passed by reference, wrap it inside `ByRef()`. For example,
```
InvokeArgument<2>(5, string("Hi"), ByRef(foo))
```
calls the mock function's #2 argument, passing to it `5` and `string("Hi")` by value, and `foo` by reference.
## Default Action ##
|`DoDefault()`|Do the default action (specified by `ON_CALL()` or the built-in one).|
|:------------|:--------------------------------------------------------------------|
**Note:** due to technical reasons, `DoDefault()` cannot be used inside a composite action - trying to do so will result in a run-time error.
## Composite Actions ##
|`DoAll(a1, a2, ..., an)`|Do all actions `a1` to `an` and return the result of `an` in each invocation. The first `n - 1` sub-actions must return void. |
|:-----------------------|:-----------------------------------------------------------------------------------------------------------------------------|
|`IgnoreResult(a)` |Perform action `a` and ignore its result. `a` must not return void. |
|`WithArg<N>(a)` |Pass the `N`-th (0-based) argument of the mock function to action `a` and perform it. |
|`WithArgs<N1, N2, ..., Nk>(a)`|Pass the selected (0-based) arguments of the mock function to action `a` and perform it. |
|`WithoutArgs(a)` |Perform action `a` without any arguments. |
## Defining Actions ##
| `ACTION(Sum) { return arg0 + arg1; }` | Defines an action `Sum()` to return the sum of the mock function's argument #0 and #1. |
|:--------------------------------------|:---------------------------------------------------------------------------------------|
| `ACTION_P(Plus, n) { return arg0 + n; }` | Defines an action `Plus(n)` to return the sum of the mock function's argument #0 and `n`. |
| `ACTION_Pk(Foo, p1, ..., pk) { statements; }` | Defines a parameterized action `Foo(p1, ..., pk)` to execute the given `statements`. |
The `ACTION*` macros cannot be used inside a function or class.
# Cardinalities #
These are used in `Times()` to specify how many times a mock function will be called:
|`AnyNumber()`|The function can be called any number of times.|
|:------------|:----------------------------------------------|
|`AtLeast(n)` |The call is expected at least `n` times. |
|`AtMost(n)` |The call is expected at most `n` times. |
|`Between(m, n)`|The call is expected between `m` and `n` (inclusive) times.|
|`Exactly(n) or n`|The call is expected exactly `n` times. In particular, the call should never happen when `n` is 0.|
# Expectation Order #
By default, the expectations can be matched in _any_ order. If some
or all expectations must be matched in a given order, there are two
ways to specify it. They can be used either independently or
together.
## The After Clause ##
```
using ::testing::Expectation;
...
Expectation init_x = EXPECT_CALL(foo, InitX());
Expectation init_y = EXPECT_CALL(foo, InitY());
EXPECT_CALL(foo, Bar())
.After(init_x, init_y);
```
says that `Bar()` can be called only after both `InitX()` and
`InitY()` have been called.
If you don't know how many pre-requisites an expectation has when you
write it, you can use an `ExpectationSet` to collect them:
```
using ::testing::ExpectationSet;
...
ExpectationSet all_inits;
for (int i = 0; i < element_count; i++) {
all_inits += EXPECT_CALL(foo, InitElement(i));
}
EXPECT_CALL(foo, Bar())
.After(all_inits);
```
says that `Bar()` can be called only after all elements have been
initialized (but we don't care about which elements get initialized
before the others).
Modifying an `ExpectationSet` after using it in an `.After()` doesn't
affect the meaning of the `.After()`.
## Sequences ##
When you have a long chain of sequential expectations, it's easier to
specify the order using **sequences**, which don't require you to given
each expectation in the chain a different name. <i>All expected<br>
calls</i> in the same sequence must occur in the order they are
specified.
```
using ::testing::Sequence;
Sequence s1, s2;
...
EXPECT_CALL(foo, Reset())
.InSequence(s1, s2)
.WillOnce(Return(true));
EXPECT_CALL(foo, GetSize())
.InSequence(s1)
.WillOnce(Return(1));
EXPECT_CALL(foo, Describe(A<const char*>()))
.InSequence(s2)
.WillOnce(Return("dummy"));
```
says that `Reset()` must be called before _both_ `GetSize()` _and_
`Describe()`, and the latter two can occur in any order.
To put many expectations in a sequence conveniently:
```
using ::testing::InSequence;
{
InSequence dummy;
EXPECT_CALL(...)...;
EXPECT_CALL(...)...;
...
EXPECT_CALL(...)...;
}
```
says that all expected calls in the scope of `dummy` must occur in
strict order. The name `dummy` is irrelevant.)
# Verifying and Resetting a Mock #
Google Mock will verify the expectations on a mock object when it is destructed, or you can do it earlier:
```
using ::testing::Mock;
...
// Verifies and removes the expectations on mock_obj;
// returns true iff successful.
Mock::VerifyAndClearExpectations(&mock_obj);
...
// Verifies and removes the expectations on mock_obj;
// also removes the default actions set by ON_CALL();
// returns true iff successful.
Mock::VerifyAndClear(&mock_obj);
```
You can also tell Google Mock that a mock object can be leaked and doesn't
need to be verified:
```
Mock::AllowLeak(&mock_obj);
```
# Mock Classes #
Google Mock defines a convenient mock class template
```
class MockFunction<R(A1, ..., An)> {
public:
MOCK_METHODn(Call, R(A1, ..., An));
};
```
See this [recipe](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Using_Check_Points) for one application of it.
# Flags #
| `--gmock_catch_leaked_mocks=0` | Don't report leaked mock objects as failures. |
|:-------------------------------|:----------------------------------------------|
| `--gmock_verbose=LEVEL` | Sets the default verbosity level (`info`, `warning`, or `error`) of Google Mock messages. |

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This page lists all documentation wiki pages for Google Mock **1.6**
- **if you use a released version of Google Mock, please read the documentation for that specific version instead.**
* [ForDummies](V1_6_ForDummies.md) -- start here if you are new to Google Mock.
* [CheatSheet](V1_6_CheatSheet.md) -- a quick reference.
* [CookBook](V1_6_CookBook.md) -- recipes for doing various tasks using Google Mock.
* [FrequentlyAskedQuestions](V1_6_FrequentlyAskedQuestions.md) -- check here before asking a question on the mailing list.
To contribute code to Google Mock, read:
* [DevGuide](DevGuide.md) -- read this _before_ writing your first patch.
* [Pump Manual](http://code.google.com/p/googletest/wiki/V1_6_PumpManual) -- how we generate some of Google Mock's source files.

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(**Note:** If you get compiler errors that you don't understand, be sure to consult [Google Mock Doctor](http://code.google.com/p/googlemock/wiki/V1_6_FrequentlyAskedQuestions#How_am_I_supposed_to_make_sense_of_these_horrible_template_error).)
# What Is Google C++ Mocking Framework? #
When you write a prototype or test, often it's not feasible or wise to rely on real objects entirely. A **mock object** implements the same interface as a real object (so it can be used as one), but lets you specify at run time how it will be used and what it should do (which methods will be called? in which order? how many times? with what arguments? what will they return? etc).
**Note:** It is easy to confuse the term _fake objects_ with mock objects. Fakes and mocks actually mean very different things in the Test-Driven Development (TDD) community:
* **Fake** objects have working implementations, but usually take some shortcut (perhaps to make the operations less expensive), which makes them not suitable for production. An in-memory file system would be an example of a fake.
* **Mocks** are objects pre-programmed with _expectations_, which form a specification of the calls they are expected to receive.
If all this seems too abstract for you, don't worry - the most important thing to remember is that a mock allows you to check the _interaction_ between itself and code that uses it. The difference between fakes and mocks will become much clearer once you start to use mocks.
**Google C++ Mocking Framework** (or **Google Mock** for short) is a library (sometimes we also call it a "framework" to make it sound cool) for creating mock classes and using them. It does to C++ what [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/) do to Java.
Using Google Mock involves three basic steps:
1. Use some simple macros to describe the interface you want to mock, and they will expand to the implementation of your mock class;
1. Create some mock objects and specify its expectations and behavior using an intuitive syntax;
1. Exercise code that uses the mock objects. Google Mock will catch any violation of the expectations as soon as it arises.
# Why Google Mock? #
While mock objects help you remove unnecessary dependencies in tests and make them fast and reliable, using mocks manually in C++ is _hard_:
* Someone has to implement the mocks. The job is usually tedious and error-prone. No wonder people go great distance to avoid it.
* The quality of those manually written mocks is a bit, uh, unpredictable. You may see some really polished ones, but you may also see some that were hacked up in a hurry and have all sorts of ad hoc restrictions.
* The knowledge you gained from using one mock doesn't transfer to the next.
In contrast, Java and Python programmers have some fine mock frameworks, which automate the creation of mocks. As a result, mocking is a proven effective technique and widely adopted practice in those communities. Having the right tool absolutely makes the difference.
Google Mock was built to help C++ programmers. It was inspired by [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/), but designed with C++'s specifics in mind. It is your friend if any of the following problems is bothering you:
* You are stuck with a sub-optimal design and wish you had done more prototyping before it was too late, but prototyping in C++ is by no means "rapid".
* Your tests are slow as they depend on too many libraries or use expensive resources (e.g. a database).
* Your tests are brittle as some resources they use are unreliable (e.g. the network).
* You want to test how your code handles a failure (e.g. a file checksum error), but it's not easy to cause one.
* You need to make sure that your module interacts with other modules in the right way, but it's hard to observe the interaction; therefore you resort to observing the side effects at the end of the action, which is awkward at best.
* You want to "mock out" your dependencies, except that they don't have mock implementations yet; and, frankly, you aren't thrilled by some of those hand-written mocks.
We encourage you to use Google Mock as:
* a _design_ tool, for it lets you experiment with your interface design early and often. More iterations lead to better designs!
* a _testing_ tool to cut your tests' outbound dependencies and probe the interaction between your module and its collaborators.
# Getting Started #
Using Google Mock is easy! Inside your C++ source file, just `#include` `"gtest/gtest.h"` and `"gmock/gmock.h"`, and you are ready to go.
# A Case for Mock Turtles #
Let's look at an example. Suppose you are developing a graphics program that relies on a LOGO-like API for drawing. How would you test that it does the right thing? Well, you can run it and compare the screen with a golden screen snapshot, but let's admit it: tests like this are expensive to run and fragile (What if you just upgraded to a shiny new graphics card that has better anti-aliasing? Suddenly you have to update all your golden images.). It would be too painful if all your tests are like this. Fortunately, you learned about Dependency Injection and know the right thing to do: instead of having your application talk to the drawing API directly, wrap the API in an interface (say, `Turtle`) and code to that interface:
```
class Turtle {
...
virtual ~Turtle() {}
virtual void PenUp() = 0;
virtual void PenDown() = 0;
virtual void Forward(int distance) = 0;
virtual void Turn(int degrees) = 0;
virtual void GoTo(int x, int y) = 0;
virtual int GetX() const = 0;
virtual int GetY() const = 0;
};
```
(Note that the destructor of `Turtle` **must** be virtual, as is the case for **all** classes you intend to inherit from - otherwise the destructor of the derived class will not be called when you delete an object through a base pointer, and you'll get corrupted program states like memory leaks.)
You can control whether the turtle's movement will leave a trace using `PenUp()` and `PenDown()`, and control its movement using `Forward()`, `Turn()`, and `GoTo()`. Finally, `GetX()` and `GetY()` tell you the current position of the turtle.
Your program will normally use a real implementation of this interface. In tests, you can use a mock implementation instead. This allows you to easily check what drawing primitives your program is calling, with what arguments, and in which order. Tests written this way are much more robust (they won't break because your new machine does anti-aliasing differently), easier to read and maintain (the intent of a test is expressed in the code, not in some binary images), and run _much, much faster_.
# Writing the Mock Class #
If you are lucky, the mocks you need to use have already been implemented by some nice people. If, however, you find yourself in the position to write a mock class, relax - Google Mock turns this task into a fun game! (Well, almost.)
## How to Define It ##
Using the `Turtle` interface as example, here are the simple steps you need to follow:
1. Derive a class `MockTurtle` from `Turtle`.
1. Take a _virtual_ function of `Turtle` (while it's possible to [mock non-virtual methods using templates](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Mocking_Nonvirtual_Methods), it's much more involved). Count how many arguments it has.
1. In the `public:` section of the child class, write `MOCK_METHODn();` (or `MOCK_CONST_METHODn();` if you are mocking a `const` method), where `n` is the number of the arguments; if you counted wrong, shame on you, and a compiler error will tell you so.
1. Now comes the fun part: you take the function signature, cut-and-paste the _function name_ as the _first_ argument to the macro, and leave what's left as the _second_ argument (in case you're curious, this is the _type of the function_).
1. Repeat until all virtual functions you want to mock are done.
After the process, you should have something like:
```
#include "gmock/gmock.h" // Brings in Google Mock.
class MockTurtle : public Turtle {
public:
...
MOCK_METHOD0(PenUp, void());
MOCK_METHOD0(PenDown, void());
MOCK_METHOD1(Forward, void(int distance));
MOCK_METHOD1(Turn, void(int degrees));
MOCK_METHOD2(GoTo, void(int x, int y));
MOCK_CONST_METHOD0(GetX, int());
MOCK_CONST_METHOD0(GetY, int());
};
```
You don't need to define these mock methods somewhere else - the `MOCK_METHOD*` macros will generate the definitions for you. It's that simple! Once you get the hang of it, you can pump out mock classes faster than your source-control system can handle your check-ins.
**Tip:** If even this is too much work for you, you'll find the
`gmock_gen.py` tool in Google Mock's `scripts/generator/` directory (courtesy of the [cppclean](http://code.google.com/p/cppclean/) project) useful. This command-line
tool requires that you have Python 2.4 installed. You give it a C++ file and the name of an abstract class defined in it,
and it will print the definition of the mock class for you. Due to the
complexity of the C++ language, this script may not always work, but
it can be quite handy when it does. For more details, read the [user documentation](http://code.google.com/p/googlemock/source/browse/trunk/scripts/generator/README).
## Where to Put It ##
When you define a mock class, you need to decide where to put its definition. Some people put it in a `*_test.cc`. This is fine when the interface being mocked (say, `Foo`) is owned by the same person or team. Otherwise, when the owner of `Foo` changes it, your test could break. (You can't really expect `Foo`'s maintainer to fix every test that uses `Foo`, can you?)
So, the rule of thumb is: if you need to mock `Foo` and it's owned by others, define the mock class in `Foo`'s package (better, in a `testing` sub-package such that you can clearly separate production code and testing utilities), and put it in a `mock_foo.h`. Then everyone can reference `mock_foo.h` from their tests. If `Foo` ever changes, there is only one copy of `MockFoo` to change, and only tests that depend on the changed methods need to be fixed.
Another way to do it: you can introduce a thin layer `FooAdaptor` on top of `Foo` and code to this new interface. Since you own `FooAdaptor`, you can absorb changes in `Foo` much more easily. While this is more work initially, carefully choosing the adaptor interface can make your code easier to write and more readable (a net win in the long run), as you can choose `FooAdaptor` to fit your specific domain much better than `Foo` does.
# Using Mocks in Tests #
Once you have a mock class, using it is easy. The typical work flow is:
1. Import the Google Mock names from the `testing` namespace such that you can use them unqualified (You only have to do it once per file. Remember that namespaces are a good idea and good for your health.).
1. Create some mock objects.
1. Specify your expectations on them (How many times will a method be called? With what arguments? What should it do? etc.).
1. Exercise some code that uses the mocks; optionally, check the result using Google Test assertions. If a mock method is called more than expected or with wrong arguments, you'll get an error immediately.
1. When a mock is destructed, Google Mock will automatically check whether all expectations on it have been satisfied.
Here's an example:
```
#include "path/to/mock-turtle.h"
#include "gmock/gmock.h"
#include "gtest/gtest.h"
using ::testing::AtLeast; // #1
TEST(PainterTest, CanDrawSomething) {
MockTurtle turtle; // #2
EXPECT_CALL(turtle, PenDown()) // #3
.Times(AtLeast(1));
Painter painter(&turtle); // #4
EXPECT_TRUE(painter.DrawCircle(0, 0, 10));
} // #5
int main(int argc, char** argv) {
// The following line must be executed to initialize Google Mock
// (and Google Test) before running the tests.
::testing::InitGoogleMock(&argc, argv);
return RUN_ALL_TESTS();
}
```
As you might have guessed, this test checks that `PenDown()` is called at least once. If the `painter` object didn't call this method, your test will fail with a message like this:
```
path/to/my_test.cc:119: Failure
Actual function call count doesn't match this expectation:
Actually: never called;
Expected: called at least once.
```
**Tip 1:** If you run the test from an Emacs buffer, you can hit `<Enter>` on the line number displayed in the error message to jump right to the failed expectation.
**Tip 2:** If your mock objects are never deleted, the final verification won't happen. Therefore it's a good idea to use a heap leak checker in your tests when you allocate mocks on the heap.
**Important note:** Google Mock requires expectations to be set **before** the mock functions are called, otherwise the behavior is **undefined**. In particular, you mustn't interleave `EXPECT_CALL()`s and calls to the mock functions.
This means `EXPECT_CALL()` should be read as expecting that a call will occur _in the future_, not that a call has occurred. Why does Google Mock work like that? Well, specifying the expectation beforehand allows Google Mock to report a violation as soon as it arises, when the context (stack trace, etc) is still available. This makes debugging much easier.
Admittedly, this test is contrived and doesn't do much. You can easily achieve the same effect without using Google Mock. However, as we shall reveal soon, Google Mock allows you to do _much more_ with the mocks.
## Using Google Mock with Any Testing Framework ##
If you want to use something other than Google Test (e.g. [CppUnit](http://apps.sourceforge.net/mediawiki/cppunit/index.php?title=Main_Page) or
[CxxTest](http://cxxtest.tigris.org/)) as your testing framework, just change the `main()` function in the previous section to:
```
int main(int argc, char** argv) {
// The following line causes Google Mock to throw an exception on failure,
// which will be interpreted by your testing framework as a test failure.
::testing::GTEST_FLAG(throw_on_failure) = true;
::testing::InitGoogleMock(&argc, argv);
... whatever your testing framework requires ...
}
```
This approach has a catch: it makes Google Mock throw an exception
from a mock object's destructor sometimes. With some compilers, this
sometimes causes the test program to crash. You'll still be able to
notice that the test has failed, but it's not a graceful failure.
A better solution is to use Google Test's
[event listener API](http://code.google.com/p/googletest/wiki/V1_6_AdvancedGuide#Extending_Google_Test_by_Handling_Test_Events)
to report a test failure to your testing framework properly. You'll need to
implement the `OnTestPartResult()` method of the event listener interface, but it
should be straightforward.
If this turns out to be too much work, we suggest that you stick with
Google Test, which works with Google Mock seamlessly (in fact, it is
technically part of Google Mock.). If there is a reason that you
cannot use Google Test, please let us know.
# Setting Expectations #
The key to using a mock object successfully is to set the _right expectations_ on it. If you set the expectations too strict, your test will fail as the result of unrelated changes. If you set them too loose, bugs can slip through. You want to do it just right such that your test can catch exactly the kind of bugs you intend it to catch. Google Mock provides the necessary means for you to do it "just right."
## General Syntax ##
In Google Mock we use the `EXPECT_CALL()` macro to set an expectation on a mock method. The general syntax is:
```
EXPECT_CALL(mock_object, method(matchers))
.Times(cardinality)
.WillOnce(action)
.WillRepeatedly(action);
```
The macro has two arguments: first the mock object, and then the method and its arguments. Note that the two are separated by a comma (`,`), not a period (`.`). (Why using a comma? The answer is that it was necessary for technical reasons.)
The macro can be followed by some optional _clauses_ that provide more information about the expectation. We'll discuss how each clause works in the coming sections.
This syntax is designed to make an expectation read like English. For example, you can probably guess that
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetX())
.Times(5)
.WillOnce(Return(100))
.WillOnce(Return(150))
.WillRepeatedly(Return(200));
```
says that the `turtle` object's `GetX()` method will be called five times, it will return 100 the first time, 150 the second time, and then 200 every time. Some people like to call this style of syntax a Domain-Specific Language (DSL).
**Note:** Why do we use a macro to do this? It serves two purposes: first it makes expectations easily identifiable (either by `grep` or by a human reader), and second it allows Google Mock to include the source file location of a failed expectation in messages, making debugging easier.
## Matchers: What Arguments Do We Expect? ##
When a mock function takes arguments, we must specify what arguments we are expecting; for example:
```
// Expects the turtle to move forward by 100 units.
EXPECT_CALL(turtle, Forward(100));
```
Sometimes you may not want to be too specific (Remember that talk about tests being too rigid? Over specification leads to brittle tests and obscures the intent of tests. Therefore we encourage you to specify only what's necessary - no more, no less.). If you care to check that `Forward()` will be called but aren't interested in its actual argument, write `_` as the argument, which means "anything goes":
```
using ::testing::_;
...
// Expects the turtle to move forward.
EXPECT_CALL(turtle, Forward(_));
```
`_` is an instance of what we call **matchers**. A matcher is like a predicate and can test whether an argument is what we'd expect. You can use a matcher inside `EXPECT_CALL()` wherever a function argument is expected.
A list of built-in matchers can be found in the [CheatSheet](V1_6_CheatSheet.md). For example, here's the `Ge` (greater than or equal) matcher:
```
using ::testing::Ge;...
EXPECT_CALL(turtle, Forward(Ge(100)));
```
This checks that the turtle will be told to go forward by at least 100 units.
## Cardinalities: How Many Times Will It Be Called? ##
The first clause we can specify following an `EXPECT_CALL()` is `Times()`. We call its argument a **cardinality** as it tells _how many times_ the call should occur. It allows us to repeat an expectation many times without actually writing it as many times. More importantly, a cardinality can be "fuzzy", just like a matcher can be. This allows a user to express the intent of a test exactly.
An interesting special case is when we say `Times(0)`. You may have guessed - it means that the function shouldn't be called with the given arguments at all, and Google Mock will report a Google Test failure whenever the function is (wrongfully) called.
We've seen `AtLeast(n)` as an example of fuzzy cardinalities earlier. For the list of built-in cardinalities you can use, see the [CheatSheet](V1_6_CheatSheet.md).
The `Times()` clause can be omitted. **If you omit `Times()`, Google Mock will infer the cardinality for you.** The rules are easy to remember:
* If **neither** `WillOnce()` **nor** `WillRepeatedly()` is in the `EXPECT_CALL()`, the inferred cardinality is `Times(1)`.
* If there are `n WillOnce()`'s but **no** `WillRepeatedly()`, where `n` >= 1, the cardinality is `Times(n)`.
* If there are `n WillOnce()`'s and **one** `WillRepeatedly()`, where `n` >= 0, the cardinality is `Times(AtLeast(n))`.
**Quick quiz:** what do you think will happen if a function is expected to be called twice but actually called four times?
## Actions: What Should It Do? ##
Remember that a mock object doesn't really have a working implementation? We as users have to tell it what to do when a method is invoked. This is easy in Google Mock.
First, if the return type of a mock function is a built-in type or a pointer, the function has a **default action** (a `void` function will just return, a `bool` function will return `false`, and other functions will return 0). If you don't say anything, this behavior will be used.
Second, if a mock function doesn't have a default action, or the default action doesn't suit you, you can specify the action to be taken each time the expectation matches using a series of `WillOnce()` clauses followed by an optional `WillRepeatedly()`. For example,
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillOnce(Return(300));
```
This says that `turtle.GetX()` will be called _exactly three times_ (Google Mock inferred this from how many `WillOnce()` clauses we've written, since we didn't explicitly write `Times()`), and will return 100, 200, and 300 respectively.
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetY())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillRepeatedly(Return(300));
```
says that `turtle.GetY()` will be called _at least twice_ (Google Mock knows this as we've written two `WillOnce()` clauses and a `WillRepeatedly()` while having no explicit `Times()`), will return 100 the first time, 200 the second time, and 300 from the third time on.
Of course, if you explicitly write a `Times()`, Google Mock will not try to infer the cardinality itself. What if the number you specified is larger than there are `WillOnce()` clauses? Well, after all `WillOnce()`s are used up, Google Mock will do the _default_ action for the function every time (unless, of course, you have a `WillRepeatedly()`.).
What can we do inside `WillOnce()` besides `Return()`? You can return a reference using `ReturnRef(variable)`, or invoke a pre-defined function, among [others](http://code.google.com/p/googlemock/wiki/V1_6_CheatSheet#Actions).
**Important note:** The `EXPECT_CALL()` statement evaluates the action clause only once, even though the action may be performed many times. Therefore you must be careful about side effects. The following may not do what you want:
```
int n = 100;
EXPECT_CALL(turtle, GetX())
.Times(4)
.WillRepeatedly(Return(n++));
```
Instead of returning 100, 101, 102, ..., consecutively, this mock function will always return 100 as `n++` is only evaluated once. Similarly, `Return(new Foo)` will create a new `Foo` object when the `EXPECT_CALL()` is executed, and will return the same pointer every time. If you want the side effect to happen every time, you need to define a custom action, which we'll teach in the [CookBook](V1_6_CookBook.md).
Time for another quiz! What do you think the following means?
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetY())
.Times(4)
.WillOnce(Return(100));
```
Obviously `turtle.GetY()` is expected to be called four times. But if you think it will return 100 every time, think twice! Remember that one `WillOnce()` clause will be consumed each time the function is invoked and the default action will be taken afterwards. So the right answer is that `turtle.GetY()` will return 100 the first time, but **return 0 from the second time on**, as returning 0 is the default action for `int` functions.
## Using Multiple Expectations ##
So far we've only shown examples where you have a single expectation. More realistically, you're going to specify expectations on multiple mock methods, which may be from multiple mock objects.
By default, when a mock method is invoked, Google Mock will search the expectations in the **reverse order** they are defined, and stop when an active expectation that matches the arguments is found (you can think of it as "newer rules override older ones."). If the matching expectation cannot take any more calls, you will get an upper-bound-violated failure. Here's an example:
```
using ::testing::_;...
EXPECT_CALL(turtle, Forward(_)); // #1
EXPECT_CALL(turtle, Forward(10)) // #2
.Times(2);
```
If `Forward(10)` is called three times in a row, the third time it will be an error, as the last matching expectation (#2) has been saturated. If, however, the third `Forward(10)` call is replaced by `Forward(20)`, then it would be OK, as now #1 will be the matching expectation.
**Side note:** Why does Google Mock search for a match in the _reverse_ order of the expectations? The reason is that this allows a user to set up the default expectations in a mock object's constructor or the test fixture's set-up phase and then customize the mock by writing more specific expectations in the test body. So, if you have two expectations on the same method, you want to put the one with more specific matchers **after** the other, or the more specific rule would be shadowed by the more general one that comes after it.
## Ordered vs Unordered Calls ##
By default, an expectation can match a call even though an earlier expectation hasn't been satisfied. In other words, the calls don't have to occur in the order the expectations are specified.
Sometimes, you may want all the expected calls to occur in a strict order. To say this in Google Mock is easy:
```
using ::testing::InSequence;...
TEST(FooTest, DrawsLineSegment) {
...
{
InSequence dummy;
EXPECT_CALL(turtle, PenDown());
EXPECT_CALL(turtle, Forward(100));
EXPECT_CALL(turtle, PenUp());
}
Foo();
}
```
By creating an object of type `InSequence`, all expectations in its scope are put into a _sequence_ and have to occur _sequentially_. Since we are just relying on the constructor and destructor of this object to do the actual work, its name is really irrelevant.
In this example, we test that `Foo()` calls the three expected functions in the order as written. If a call is made out-of-order, it will be an error.
(What if you care about the relative order of some of the calls, but not all of them? Can you specify an arbitrary partial order? The answer is ... yes! If you are impatient, the details can be found in the [CookBook](V1_6_CookBook.md).)
## All Expectations Are Sticky (Unless Said Otherwise) ##
Now let's do a quick quiz to see how well you can use this mock stuff already. How would you test that the turtle is asked to go to the origin _exactly twice_ (you want to ignore any other instructions it receives)?
After you've come up with your answer, take a look at ours and compare notes (solve it yourself first - don't cheat!):
```
using ::testing::_;...
EXPECT_CALL(turtle, GoTo(_, _)) // #1
.Times(AnyNumber());
EXPECT_CALL(turtle, GoTo(0, 0)) // #2
.Times(2);
```
Suppose `turtle.GoTo(0, 0)` is called three times. In the third time, Google Mock will see that the arguments match expectation #2 (remember that we always pick the last matching expectation). Now, since we said that there should be only two such calls, Google Mock will report an error immediately. This is basically what we've told you in the "Using Multiple Expectations" section above.
This example shows that **expectations in Google Mock are "sticky" by default**, in the sense that they remain active even after we have reached their invocation upper bounds. This is an important rule to remember, as it affects the meaning of the spec, and is **different** to how it's done in many other mocking frameworks (Why'd we do that? Because we think our rule makes the common cases easier to express and understand.).
Simple? Let's see if you've really understood it: what does the following code say?
```
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i));
}
```
If you think it says that `turtle.GetX()` will be called `n` times and will return 10, 20, 30, ..., consecutively, think twice! The problem is that, as we said, expectations are sticky. So, the second time `turtle.GetX()` is called, the last (latest) `EXPECT_CALL()` statement will match, and will immediately lead to an "upper bound exceeded" error - this piece of code is not very useful!
One correct way of saying that `turtle.GetX()` will return 10, 20, 30, ..., is to explicitly say that the expectations are _not_ sticky. In other words, they should _retire_ as soon as they are saturated:
```
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
```
And, there's a better way to do it: in this case, we expect the calls to occur in a specific order, and we line up the actions to match the order. Since the order is important here, we should make it explicit using a sequence:
```
using ::testing::InSequence;
using ::testing::Return;
...
{
InSequence s;
for (int i = 1; i <= n; i++) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
}
```
By the way, the other situation where an expectation may _not_ be sticky is when it's in a sequence - as soon as another expectation that comes after it in the sequence has been used, it automatically retires (and will never be used to match any call).
## Uninteresting Calls ##
A mock object may have many methods, and not all of them are that interesting. For example, in some tests we may not care about how many times `GetX()` and `GetY()` get called.
In Google Mock, if you are not interested in a method, just don't say anything about it. If a call to this method occurs, you'll see a warning in the test output, but it won't be a failure.
# What Now? #
Congratulations! You've learned enough about Google Mock to start using it. Now, you might want to join the [googlemock](http://groups.google.com/group/googlemock) discussion group and actually write some tests using Google Mock - it will be fun. Hey, it may even be addictive - you've been warned.
Then, if you feel like increasing your mock quotient, you should move on to the [CookBook](V1_6_CookBook.md). You can learn many advanced features of Google Mock there -- and advance your level of enjoyment and testing bliss.

628
googlemock/docs/v1_6/FrequentlyAskedQuestions.md
Unescape View File

@ -1,628 +0,0 @@
Please send your questions to the
[googlemock](http://groups.google.com/group/googlemock) discussion
group. If you need help with compiler errors, make sure you have
tried [Google Mock Doctor](#How_am_I_supposed_to_make_sense_of_these_horrible_template_error.md) first.
## When I call a method on my mock object, the method for the real object is invoked instead. What's the problem? ##
In order for a method to be mocked, it must be _virtual_, unless you use the [high-perf dependency injection technique](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Mocking_Nonvirtual_Methods).
## I wrote some matchers. After I upgraded to a new version of Google Mock, they no longer compile. What's going on? ##
After version 1.4.0 of Google Mock was released, we had an idea on how
to make it easier to write matchers that can generate informative
messages efficiently. We experimented with this idea and liked what
we saw. Therefore we decided to implement it.
Unfortunately, this means that if you have defined your own matchers
by implementing `MatcherInterface` or using `MakePolymorphicMatcher()`,
your definitions will no longer compile. Matchers defined using the
`MATCHER*` family of macros are not affected.
Sorry for the hassle if your matchers are affected. We believe it's
in everyone's long-term interest to make this change sooner than
later. Fortunately, it's usually not hard to migrate an existing
matcher to the new API. Here's what you need to do:
If you wrote your matcher like this:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
you'll need to change it to:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
(i.e. rename `Matches()` to `MatchAndExplain()` and give it a second
argument of type `MatchResultListener*`.)
If you were also using `ExplainMatchResultTo()` to improve the matcher
message:
```
// Old matcher definition that doesn't work with the lastest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
virtual void ExplainMatchResultTo(MyType value,
::std::ostream* os) const {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Foo property is " << value.GetFoo();
}
...
};
```
you should move the logic of `ExplainMatchResultTo()` into
`MatchAndExplain()`, using the `MatchResultListener` argument where
the `::std::ostream` was used:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Foo property is " << value.GetFoo();
return value.GetFoo() > 5;
}
...
};
```
If your matcher is defined using `MakePolymorphicMatcher()`:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you should rename the `Matches()` method to `MatchAndExplain()` and
add a `MatchResultListener*` argument (the same as what you need to do
for matchers defined by implementing `MatcherInterface`):
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
If your polymorphic matcher uses `ExplainMatchResultTo()` for better
failure messages:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
void ExplainMatchResultTo(const MyGreatMatcher& matcher,
MyType value,
::std::ostream* os) {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Bar property is " << value.GetBar();
}
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you'll need to move the logic inside `ExplainMatchResultTo()` to
`MatchAndExplain()`:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Bar property is " << value.GetBar();
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
For more information, you can read these
[two](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Writing_New_Monomorphic_Matchers)
[recipes](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Writing_New_Polymorphic_Matchers)
from the cookbook. As always, you
are welcome to post questions on `googlemock@googlegroups.com` if you
need any help.
## When using Google Mock, do I have to use Google Test as the testing framework? I have my favorite testing framework and don't want to switch. ##
Google Mock works out of the box with Google Test. However, it's easy
to configure it to work with any testing framework of your choice.
[Here](http://code.google.com/p/googlemock/wiki/V1_6_ForDummies#Using_Google_Mock_with_Any_Testing_Framework) is how.
## How am I supposed to make sense of these horrible template errors? ##
If you are confused by the compiler errors gcc threw at you,
try consulting the _Google Mock Doctor_ tool first. What it does is to
scan stdin for gcc error messages, and spit out diagnoses on the
problems (we call them diseases) your code has.
To "install", run command:
```
alias gmd='<path to googlemock>/scripts/gmock_doctor.py'
```
To use it, do:
```
<your-favorite-build-command> <your-test> 2>&1 | gmd
```
For example:
```
make my_test 2>&1 | gmd
```
Or you can run `gmd` and copy-n-paste gcc's error messages to it.
## Can I mock a variadic function? ##
You cannot mock a variadic function (i.e. a function taking ellipsis
(`...`) arguments) directly in Google Mock.
The problem is that in general, there is _no way_ for a mock object to
know how many arguments are passed to the variadic method, and what
the arguments' types are. Only the _author of the base class_ knows
the protocol, and we cannot look into his head.
Therefore, to mock such a function, the _user_ must teach the mock
object how to figure out the number of arguments and their types. One
way to do it is to provide overloaded versions of the function.
Ellipsis arguments are inherited from C and not really a C++ feature.
They are unsafe to use and don't work with arguments that have
constructors or destructors. Therefore we recommend to avoid them in
C++ as much as possible.
## MSVC gives me warning C4301 or C4373 when I define a mock method with a const parameter. Why? ##
If you compile this using Microsoft Visual C++ 2005 SP1:
```
class Foo {
...
virtual void Bar(const int i) = 0;
};
class MockFoo : public Foo {
...
MOCK_METHOD1(Bar, void(const int i));
};
```
You may get the following warning:
```
warning C4301: 'MockFoo::Bar': overriding virtual function only differs from 'Foo::Bar' by const/volatile qualifier
```
This is a MSVC bug. The same code compiles fine with gcc ,for
example. If you use Visual C++ 2008 SP1, you would get the warning:
```
warning C4373: 'MockFoo::Bar': virtual function overrides 'Foo::Bar', previous versions of the compiler did not override when parameters only differed by const/volatile qualifiers
```
In C++, if you _declare_ a function with a `const` parameter, the
`const` modifier is _ignored_. Therefore, the `Foo` base class above
is equivalent to:
```
class Foo {
...
virtual void Bar(int i) = 0; // int or const int? Makes no difference.
};
```
In fact, you can _declare_ Bar() with an `int` parameter, and _define_
it with a `const int` parameter. The compiler will still match them
up.
Since making a parameter `const` is meaningless in the method
_declaration_, we recommend to remove it in both `Foo` and `MockFoo`.
That should workaround the VC bug.
Note that we are talking about the _top-level_ `const` modifier here.
If the function parameter is passed by pointer or reference, declaring
the _pointee_ or _referee_ as `const` is still meaningful. For
example, the following two declarations are _not_ equivalent:
```
void Bar(int* p); // Neither p nor *p is const.
void Bar(const int* p); // p is not const, but *p is.
```
## I have a huge mock class, and Microsoft Visual C++ runs out of memory when compiling it. What can I do? ##
We've noticed that when the `/clr` compiler flag is used, Visual C++
uses 5~6 times as much memory when compiling a mock class. We suggest
to avoid `/clr` when compiling native C++ mocks.
## I can't figure out why Google Mock thinks my expectations are not satisfied. What should I do? ##
You might want to run your test with
`--gmock_verbose=info`. This flag lets Google Mock print a trace
of every mock function call it receives. By studying the trace,
you'll gain insights on why the expectations you set are not met.
## How can I assert that a function is NEVER called? ##
```
EXPECT_CALL(foo, Bar(_))
.Times(0);
```
## I have a failed test where Google Mock tells me TWICE that a particular expectation is not satisfied. Isn't this redundant? ##
When Google Mock detects a failure, it prints relevant information
(the mock function arguments, the state of relevant expectations, and
etc) to help the user debug. If another failure is detected, Google
Mock will do the same, including printing the state of relevant
expectations.
Sometimes an expectation's state didn't change between two failures,
and you'll see the same description of the state twice. They are
however _not_ redundant, as they refer to _different points in time_.
The fact they are the same _is_ interesting information.
## I get a heap check failure when using a mock object, but using a real object is fine. What can be wrong? ##
Does the class (hopefully a pure interface) you are mocking have a
virtual destructor?
Whenever you derive from a base class, make sure its destructor is
virtual. Otherwise Bad Things will happen. Consider the following
code:
```
class Base {
public:
// Not virtual, but should be.
~Base() { ... }
...
};
class Derived : public Base {
public:
...
private:
std::string value_;
};
...
Base* p = new Derived;
...
delete p; // Surprise! ~Base() will be called, but ~Derived() will not
// - value_ is leaked.
```
By changing `~Base()` to virtual, `~Derived()` will be correctly
called when `delete p` is executed, and the heap checker
will be happy.
## The "newer expectations override older ones" rule makes writing expectations awkward. Why does Google Mock do that? ##
When people complain about this, often they are referring to code like:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. However, I have to write the expectations in the
// reverse order. This sucks big time!!!
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
```
The problem is that they didn't pick the **best** way to express the test's
intent.
By default, expectations don't have to be matched in _any_ particular
order. If you want them to match in a certain order, you need to be
explicit. This is Google Mock's (and jMock's) fundamental philosophy: it's
easy to accidentally over-specify your tests, and we want to make it
harder to do so.
There are two better ways to write the test spec. You could either
put the expectations in sequence:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. Using a sequence, we can write the expectations
// in their natural order.
{
InSequence s;
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
}
```
or you can put the sequence of actions in the same expectation:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time.
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.WillOnce(Return(2))
.RetiresOnSaturation();
```
Back to the original questions: why does Google Mock search the
expectations (and `ON_CALL`s) from back to front? Because this
allows a user to set up a mock's behavior for the common case early
(e.g. in the mock's constructor or the test fixture's set-up phase)
and customize it with more specific rules later. If Google Mock
searches from front to back, this very useful pattern won't be
possible.
## Google Mock prints a warning when a function without EXPECT\_CALL is called, even if I have set its behavior using ON\_CALL. Would it be reasonable not to show the warning in this case? ##
When choosing between being neat and being safe, we lean toward the
latter. So the answer is that we think it's better to show the
warning.
Often people write `ON_CALL`s in the mock object's
constructor or `SetUp()`, as the default behavior rarely changes from
test to test. Then in the test body they set the expectations, which
are often different for each test. Having an `ON_CALL` in the set-up
part of a test doesn't mean that the calls are expected. If there's
no `EXPECT_CALL` and the method is called, it's possibly an error. If
we quietly let the call go through without notifying the user, bugs
may creep in unnoticed.
If, however, you are sure that the calls are OK, you can write
```
EXPECT_CALL(foo, Bar(_))
.WillRepeatedly(...);
```
instead of
```
ON_CALL(foo, Bar(_))
.WillByDefault(...);
```
This tells Google Mock that you do expect the calls and no warning should be
printed.
Also, you can control the verbosity using the `--gmock_verbose` flag.
If you find the output too noisy when debugging, just choose a less
verbose level.
## How can I delete the mock function's argument in an action? ##
If you find yourself needing to perform some action that's not
supported by Google Mock directly, remember that you can define your own
actions using
[MakeAction()](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Writing_New_Actions) or
[MakePolymorphicAction()](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Writing_New_Polymorphic_Actions),
or you can write a stub function and invoke it using
[Invoke()](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Using_Functions_Methods_Functors).
## MOCK\_METHODn()'s second argument looks funny. Why don't you use the MOCK\_METHODn(Method, return\_type, arg\_1, ..., arg\_n) syntax? ##
What?! I think it's beautiful. :-)
While which syntax looks more natural is a subjective matter to some
extent, Google Mock's syntax was chosen for several practical advantages it
has.
Try to mock a function that takes a map as an argument:
```
virtual int GetSize(const map<int, std::string>& m);
```
Using the proposed syntax, it would be:
```
MOCK_METHOD1(GetSize, int, const map<int, std::string>& m);
```
Guess what? You'll get a compiler error as the compiler thinks that
`const map<int, std::string>& m` are **two**, not one, arguments. To work
around this you can use `typedef` to give the map type a name, but
that gets in the way of your work. Google Mock's syntax avoids this
problem as the function's argument types are protected inside a pair
of parentheses:
```
// This compiles fine.
MOCK_METHOD1(GetSize, int(const map<int, std::string>& m));
```
You still need a `typedef` if the return type contains an unprotected
comma, but that's much rarer.
Other advantages include:
1. `MOCK_METHOD1(Foo, int, bool)` can leave a reader wonder whether the method returns `int` or `bool`, while there won't be such confusion using Google Mock's syntax.
1. The way Google Mock describes a function type is nothing new, although many people may not be familiar with it. The same syntax was used in C, and the `function` library in `tr1` uses this syntax extensively. Since `tr1` will become a part of the new version of STL, we feel very comfortable to be consistent with it.
1. The function type syntax is also used in other parts of Google Mock's API (e.g. the action interface) in order to make the implementation tractable. A user needs to learn it anyway in order to utilize Google Mock's more advanced features. We'd as well stick to the same syntax in `MOCK_METHOD*`!
## My code calls a static/global function. Can I mock it? ##
You can, but you need to make some changes.
In general, if you find yourself needing to mock a static function,
it's a sign that your modules are too tightly coupled (and less
flexible, less reusable, less testable, etc). You are probably better
off defining a small interface and call the function through that
interface, which then can be easily mocked. It's a bit of work
initially, but usually pays for itself quickly.
This Google Testing Blog
[post](http://googletesting.blogspot.com/2008/06/defeat-static-cling.html)
says it excellently. Check it out.
## My mock object needs to do complex stuff. It's a lot of pain to specify the actions. Google Mock sucks! ##
I know it's not a question, but you get an answer for free any way. :-)
With Google Mock, you can create mocks in C++ easily. And people might be
tempted to use them everywhere. Sometimes they work great, and
sometimes you may find them, well, a pain to use. So, what's wrong in
the latter case?
When you write a test without using mocks, you exercise the code and
assert that it returns the correct value or that the system is in an
expected state. This is sometimes called "state-based testing".
Mocks are great for what some call "interaction-based" testing:
instead of checking the system state at the very end, mock objects
verify that they are invoked the right way and report an error as soon
as it arises, giving you a handle on the precise context in which the
error was triggered. This is often more effective and economical to
do than state-based testing.
If you are doing state-based testing and using a test double just to
simulate the real object, you are probably better off using a fake.
Using a mock in this case causes pain, as it's not a strong point for
mocks to perform complex actions. If you experience this and think
that mocks suck, you are just not using the right tool for your
problem. Or, you might be trying to solve the wrong problem. :-)
## I got a warning "Uninteresting function call encountered - default action taken.." Should I panic? ##
By all means, NO! It's just an FYI.
What it means is that you have a mock function, you haven't set any
expectations on it (by Google Mock's rule this means that you are not
interested in calls to this function and therefore it can be called
any number of times), and it is called. That's OK - you didn't say
it's not OK to call the function!
What if you actually meant to disallow this function to be called, but
forgot to write `EXPECT_CALL(foo, Bar()).Times(0)`? While
one can argue that it's the user's fault, Google Mock tries to be nice and
prints you a note.
So, when you see the message and believe that there shouldn't be any
uninteresting calls, you should investigate what's going on. To make
your life easier, Google Mock prints the function name and arguments
when an uninteresting call is encountered.
## I want to define a custom action. Should I use Invoke() or implement the action interface? ##
Either way is fine - you want to choose the one that's more convenient
for your circumstance.
Usually, if your action is for a particular function type, defining it
using `Invoke()` should be easier; if your action can be used in
functions of different types (e.g. if you are defining
`Return(value)`), `MakePolymorphicAction()` is
easiest. Sometimes you want precise control on what types of
functions the action can be used in, and implementing
`ActionInterface` is the way to go here. See the implementation of
`Return()` in `include/gmock/gmock-actions.h` for an example.
## I'm using the set-argument-pointee action, and the compiler complains about "conflicting return type specified". What does it mean? ##
You got this error as Google Mock has no idea what value it should return
when the mock method is called. `SetArgPointee()` says what the
side effect is, but doesn't say what the return value should be. You
need `DoAll()` to chain a `SetArgPointee()` with a `Return()`.
See this [recipe](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Mocking_Side_Effects) for more details and an example.
## My question is not in your FAQ! ##
If you cannot find the answer to your question in this FAQ, there are
some other resources you can use:
1. read other [wiki pages](http://code.google.com/p/googlemock/w/list),
1. search the mailing list [archive](http://groups.google.com/group/googlemock/topics),
1. ask it on [googlemock@googlegroups.com](mailto:googlemock@googlegroups.com) and someone will answer it (to prevent spam, we require you to join the [discussion group](http://groups.google.com/group/googlemock) before you can post.).
Please note that creating an issue in the
[issue tracker](http://code.google.com/p/googlemock/issues/list) is _not_
a good way to get your answer, as it is monitored infrequently by a
very small number of people.
When asking a question, it's helpful to provide as much of the
following information as possible (people cannot help you if there's
not enough information in your question):
* the version (or the revision number if you check out from SVN directly) of Google Mock you use (Google Mock is under active development, so it's possible that your problem has been solved in a later version),
* your operating system,
* the name and version of your compiler,
* the complete command line flags you give to your compiler,
* the complete compiler error messages (if the question is about compilation),
* the _actual_ code (ideally, a minimal but complete program) that has the problem you encounter.

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# Defining a Mock Class #
## Mocking a Normal Class ##
Given
```
class Foo {
...
virtual ~Foo();
virtual int GetSize() const = 0;
virtual string Describe(const char* name) = 0;
virtual string Describe(int type) = 0;
virtual bool Process(Bar elem, int count) = 0;
};
```
(note that `~Foo()` **must** be virtual) we can define its mock as
```
#include "gmock/gmock.h"
class MockFoo : public Foo {
MOCK_CONST_METHOD0(GetSize, int());
MOCK_METHOD1(Describe, string(const char* name));
MOCK_METHOD1(Describe, string(int type));
MOCK_METHOD2(Process, bool(Bar elem, int count));
};
```
To create a "nice" mock object which ignores all uninteresting calls,
or a "strict" mock object, which treats them as failures:
```
NiceMock<MockFoo> nice_foo; // The type is a subclass of MockFoo.
StrictMock<MockFoo> strict_foo; // The type is a subclass of MockFoo.
```
## Mocking a Class Template ##
To mock
```
template <typename Elem>
class StackInterface {
public:
...
virtual ~StackInterface();
virtual int GetSize() const = 0;
virtual void Push(const Elem& x) = 0;
};
```
(note that `~StackInterface()` **must** be virtual) just append `_T` to the `MOCK_*` macros:
```
template <typename Elem>
class MockStack : public StackInterface<Elem> {
public:
...
MOCK_CONST_METHOD0_T(GetSize, int());
MOCK_METHOD1_T(Push, void(const Elem& x));
};
```
## Specifying Calling Conventions for Mock Functions ##
If your mock function doesn't use the default calling convention, you
can specify it by appending `_WITH_CALLTYPE` to any of the macros
described in the previous two sections and supplying the calling
convention as the first argument to the macro. For example,
```
MOCK_METHOD_1_WITH_CALLTYPE(STDMETHODCALLTYPE, Foo, bool(int n));
MOCK_CONST_METHOD2_WITH_CALLTYPE(STDMETHODCALLTYPE, Bar, int(double x, double y));
```
where `STDMETHODCALLTYPE` is defined by `<objbase.h>` on Windows.
# Using Mocks in Tests #
The typical flow is:
1. Import the Google Mock names you need to use. All Google Mock names are in the `testing` namespace unless they are macros or otherwise noted.
1. Create the mock objects.
1. Optionally, set the default actions of the mock objects.
1. Set your expectations on the mock objects (How will they be called? What wil they do?).
1. Exercise code that uses the mock objects; if necessary, check the result using [Google Test](http://code.google.com/p/googletest/) assertions.
1. When a mock objects is destructed, Google Mock automatically verifies that all expectations on it have been satisfied.
Here is an example:
```
using ::testing::Return; // #1
TEST(BarTest, DoesThis) {
MockFoo foo; // #2
ON_CALL(foo, GetSize()) // #3
.WillByDefault(Return(1));
// ... other default actions ...
EXPECT_CALL(foo, Describe(5)) // #4
.Times(3)
.WillRepeatedly(Return("Category 5"));
// ... other expectations ...
EXPECT_EQ("good", MyProductionFunction(&foo)); // #5
} // #6
```
# Setting Default Actions #
Google Mock has a **built-in default action** for any function that
returns `void`, `bool`, a numeric value, or a pointer.
To customize the default action for functions with return type `T` globally:
```
using ::testing::DefaultValue;
DefaultValue<T>::Set(value); // Sets the default value to be returned.
// ... use the mocks ...
DefaultValue<T>::Clear(); // Resets the default value.
```
To customize the default action for a particular method, use `ON_CALL()`:
```
ON_CALL(mock_object, method(matchers))
.With(multi_argument_matcher) ?
.WillByDefault(action);
```
# Setting Expectations #
`EXPECT_CALL()` sets **expectations** on a mock method (How will it be
called? What will it do?):
```
EXPECT_CALL(mock_object, method(matchers))
.With(multi_argument_matcher) ?
.Times(cardinality) ?
.InSequence(sequences) *
.After(expectations) *
.WillOnce(action) *
.WillRepeatedly(action) ?
.RetiresOnSaturation(); ?
```
If `Times()` is omitted, the cardinality is assumed to be:
* `Times(1)` when there is neither `WillOnce()` nor `WillRepeatedly()`;
* `Times(n)` when there are `n WillOnce()`s but no `WillRepeatedly()`, where `n` >= 1; or
* `Times(AtLeast(n))` when there are `n WillOnce()`s and a `WillRepeatedly()`, where `n` >= 0.
A method with no `EXPECT_CALL()` is free to be invoked _any number of times_, and the default action will be taken each time.
# Matchers #
A **matcher** matches a _single_ argument. You can use it inside
`ON_CALL()` or `EXPECT_CALL()`, or use it to validate a value
directly:
| `EXPECT_THAT(value, matcher)` | Asserts that `value` matches `matcher`. |
|:------------------------------|:----------------------------------------|
| `ASSERT_THAT(value, matcher)` | The same as `EXPECT_THAT(value, matcher)`, except that it generates a **fatal** failure. |
Built-in matchers (where `argument` is the function argument) are
divided into several categories:
## Wildcard ##
|`_`|`argument` can be any value of the correct type.|
|:--|:-----------------------------------------------|
|`A<type>()` or `An<type>()`|`argument` can be any value of type `type`. |
## Generic Comparison ##
|`Eq(value)` or `value`|`argument == value`|
|:---------------------|:------------------|
|`Ge(value)` |`argument >= value`|
|`Gt(value)` |`argument > value` |
|`Le(value)` |`argument <= value`|
|`Lt(value)` |`argument < value` |
|`Ne(value)` |`argument != value`|
|`IsNull()` |`argument` is a `NULL` pointer (raw or smart).|
|`NotNull()` |`argument` is a non-null pointer (raw or smart).|
|`Ref(variable)` |`argument` is a reference to `variable`.|
|`TypedEq<type>(value)`|`argument` has type `type` and is equal to `value`. You may need to use this instead of `Eq(value)` when the mock function is overloaded.|
Except `Ref()`, these matchers make a _copy_ of `value` in case it's
modified or destructed later. If the compiler complains that `value`
doesn't have a public copy constructor, try wrap it in `ByRef()`,
e.g. `Eq(ByRef(non_copyable_value))`. If you do that, make sure
`non_copyable_value` is not changed afterwards, or the meaning of your
matcher will be changed.
## Floating-Point Matchers ##
|`DoubleEq(a_double)`|`argument` is a `double` value approximately equal to `a_double`, treating two NaNs as unequal.|
|:-------------------|:----------------------------------------------------------------------------------------------|
|`FloatEq(a_float)` |`argument` is a `float` value approximately equal to `a_float`, treating two NaNs as unequal. |
|`NanSensitiveDoubleEq(a_double)`|`argument` is a `double` value approximately equal to `a_double`, treating two NaNs as equal. |
|`NanSensitiveFloatEq(a_float)`|`argument` is a `float` value approximately equal to `a_float`, treating two NaNs as equal. |
The above matchers use ULP-based comparison (the same as used in
[Google Test](http://code.google.com/p/googletest/)). They
automatically pick a reasonable error bound based on the absolute
value of the expected value. `DoubleEq()` and `FloatEq()` conform to
the IEEE standard, which requires comparing two NaNs for equality to
return false. The `NanSensitive*` version instead treats two NaNs as
equal, which is often what a user wants.
|`DoubleNear(a_double, max_abs_error)`|`argument` is a `double` value close to `a_double` (absolute error <= `max_abs_error`), treating two NaNs as unequal.|
|:------------------------------------|:--------------------------------------------------------------------------------------------------------------------|
|`FloatNear(a_float, max_abs_error)` |`argument` is a `float` value close to `a_float` (absolute error <= `max_abs_error`), treating two NaNs as unequal. |
|`NanSensitiveDoubleNear(a_double, max_abs_error)`|`argument` is a `double` value close to `a_double` (absolute error <= `max_abs_error`), treating two NaNs as equal. |
|`NanSensitiveFloatNear(a_float, max_abs_error)`|`argument` is a `float` value close to `a_float` (absolute error <= `max_abs_error`), treating two NaNs as equal. |
## String Matchers ##
The `argument` can be either a C string or a C++ string object:
|`ContainsRegex(string)`|`argument` matches the given regular expression.|
|:----------------------|:-----------------------------------------------|
|`EndsWith(suffix)` |`argument` ends with string `suffix`. |
|`HasSubstr(string)` |`argument` contains `string` as a sub-string. |
|`MatchesRegex(string)` |`argument` matches the given regular expression with the match starting at the first character and ending at the last character.|
|`StartsWith(prefix)` |`argument` starts with string `prefix`. |
|`StrCaseEq(string)` |`argument` is equal to `string`, ignoring case. |
|`StrCaseNe(string)` |`argument` is not equal to `string`, ignoring case.|
|`StrEq(string)` |`argument` is equal to `string`. |
|`StrNe(string)` |`argument` is not equal to `string`. |
`ContainsRegex()` and `MatchesRegex()` use the regular expression
syntax defined
[here](http://code.google.com/p/googletest/wiki/AdvancedGuide#Regular_Expression_Syntax).
`StrCaseEq()`, `StrCaseNe()`, `StrEq()`, and `StrNe()` work for wide
strings as well.
## Container Matchers ##
Most STL-style containers support `==`, so you can use
`Eq(expected_container)` or simply `expected_container` to match a
container exactly. If you want to write the elements in-line,
match them more flexibly, or get more informative messages, you can use:
| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. |
|:-------------------------|:---------------------------------------------------------------------------------------------------------------------------------|
| `Contains(e)` | `argument` contains an element that matches `e`, which can be either a value or a matcher. |
| `Each(e)` | `argument` is a container where _every_ element matches `e`, which can be either a value or a matcher. |
| `ElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, where the i-th element matches `ei`, which can be a value or a matcher. 0 to 10 arguments are allowed. |
| `ElementsAreArray({ e0, e1, ..., en })`, `ElementsAreArray(array)`, or `ElementsAreArray(array, count)` | The same as `ElementsAre()` except that the expected element values/matchers come from an initializer list, vector, or C-style array. |
| `IsEmpty()` | `argument` is an empty container (`container.empty()`). |
| `Pointwise(m, container)` | `argument` contains the same number of elements as in `container`, and for all i, (the i-th element in `argument`, the i-th element in `container`) match `m`, which is a matcher on 2-tuples. E.g. `Pointwise(Le(), upper_bounds)` verifies that each element in `argument` doesn't exceed the corresponding element in `upper_bounds`. See more detail below. |
| `SizeIs(m)` | `argument` is a container whose size matches `m`. E.g. `SizeIs(2)` or `SizeIs(Lt(2))`. |
| `UnorderedElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, and under some permutation each element matches an `ei` (for a different `i`), which can be a value or a matcher. 0 to 10 arguments are allowed. |
| `UnorderedElementsAreArray({ e0, e1, ..., en })`, `UnorderedElementsAreArray(array)`, or `UnorderedElementsAreArray(array, count)` | The same as `UnorderedElementsAre()` except that the expected element values/matchers come from an initializer list, vector, or C-style array. |
| `WhenSorted(m)` | When `argument` is sorted using the `<` operator, it matches container matcher `m`. E.g. `WhenSorted(UnorderedElementsAre(1, 2, 3))` verifies that `argument` contains elements `1`, `2`, and `3`, ignoring order. |
| `WhenSortedBy(comparator, m)` | The same as `WhenSorted(m)`, except that the given comparator instead of `<` is used to sort `argument`. E.g. `WhenSortedBy(std::greater<int>(), ElementsAre(3, 2, 1))`. |
Notes:
* These matchers can also match:
1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`), and
1. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer, int len)` -- see [Multi-argument Matchers](#Multiargument_Matchers.md)).
* The array being matched may be multi-dimensional (i.e. its elements can be arrays).
* `m` in `Pointwise(m, ...)` should be a matcher for `std::tr1::tuple<T, U>` where `T` and `U` are the element type of the actual container and the expected container, respectively. For example, to compare two `Foo` containers where `Foo` doesn't support `operator==` but has an `Equals()` method, one might write:
```
using ::std::tr1::get;
MATCHER(FooEq, "") {
return get<0>(arg).Equals(get<1>(arg));
}
...
EXPECT_THAT(actual_foos, Pointwise(FooEq(), expected_foos));
```
## Member Matchers ##
|`Field(&class::field, m)`|`argument.field` (or `argument->field` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_.|
|:------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------|
|`Key(e)` |`argument.first` matches `e`, which can be either a value or a matcher. E.g. `Contains(Key(Le(5)))` can verify that a `map` contains a key `<= 5`.|
|`Pair(m1, m2)` |`argument` is an `std::pair` whose `first` field matches `m1` and `second` field matches `m2`. |
|`Property(&class::property, m)`|`argument.property()` (or `argument->property()` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_.|
## Matching the Result of a Function or Functor ##
|`ResultOf(f, m)`|`f(argument)` matches matcher `m`, where `f` is a function or functor.|
|:---------------|:---------------------------------------------------------------------|
## Pointer Matchers ##
|`Pointee(m)`|`argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`.|
|:-----------|:-----------------------------------------------------------------------------------------------|
## Multiargument Matchers ##
Technically, all matchers match a _single_ value. A "multi-argument"
matcher is just one that matches a _tuple_. The following matchers can
be used to match a tuple `(x, y)`:
|`Eq()`|`x == y`|
|:-----|:-------|
|`Ge()`|`x >= y`|
|`Gt()`|`x > y` |
|`Le()`|`x <= y`|
|`Lt()`|`x < y` |
|`Ne()`|`x != y`|
You can use the following selectors to pick a subset of the arguments
(or reorder them) to participate in the matching:
|`AllArgs(m)`|Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`.|
|:-----------|:-------------------------------------------------------------------|
|`Args<N1, N2, ..., Nk>(m)`|The tuple of the `k` selected (using 0-based indices) arguments matches `m`, e.g. `Args<1, 2>(Eq())`.|
## Composite Matchers ##
You can make a matcher from one or more other matchers:
|`AllOf(m1, m2, ..., mn)`|`argument` matches all of the matchers `m1` to `mn`.|
|:-----------------------|:---------------------------------------------------|
|`AnyOf(m1, m2, ..., mn)`|`argument` matches at least one of the matchers `m1` to `mn`.|
|`Not(m)` |`argument` doesn't match matcher `m`. |
## Adapters for Matchers ##
|`MatcherCast<T>(m)`|casts matcher `m` to type `Matcher<T>`.|
|:------------------|:--------------------------------------|
|`SafeMatcherCast<T>(m)`| [safely casts](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Casting_Matchers) matcher `m` to type `Matcher<T>`. |
|`Truly(predicate)` |`predicate(argument)` returns something considered by C++ to be true, where `predicate` is a function or functor.|
## Matchers as Predicates ##
|`Matches(m)(value)`|evaluates to `true` if `value` matches `m`. You can use `Matches(m)` alone as a unary functor.|
|:------------------|:---------------------------------------------------------------------------------------------|
|`ExplainMatchResult(m, value, result_listener)`|evaluates to `true` if `value` matches `m`, explaining the result to `result_listener`. |
|`Value(value, m)` |evaluates to `true` if `value` matches `m`. |
## Defining Matchers ##
| `MATCHER(IsEven, "") { return (arg % 2) == 0; }` | Defines a matcher `IsEven()` to match an even number. |
|:-------------------------------------------------|:------------------------------------------------------|
| `MATCHER_P(IsDivisibleBy, n, "") { *result_listener << "where the remainder is " << (arg % n); return (arg % n) == 0; }` | Defines a macher `IsDivisibleBy(n)` to match a number divisible by `n`. |
| `MATCHER_P2(IsBetween, a, b, std::string(negation ? "isn't" : "is") + " between " + PrintToString(a) + " and " + PrintToString(b)) { return a <= arg && arg <= b; }` | Defines a matcher `IsBetween(a, b)` to match a value in the range [`a`, `b`]. |
**Notes:**
1. The `MATCHER*` macros cannot be used inside a function or class.
1. The matcher body must be _purely functional_ (i.e. it cannot have any side effect, and the result must not depend on anything other than the value being matched and the matcher parameters).
1. You can use `PrintToString(x)` to convert a value `x` of any type to a string.
## Matchers as Test Assertions ##
|`ASSERT_THAT(expression, m)`|Generates a [fatal failure](http://code.google.com/p/googletest/wiki/Primer#Assertions) if the value of `expression` doesn't match matcher `m`.|
|:---------------------------|:----------------------------------------------------------------------------------------------------------------------------------------------|
|`EXPECT_THAT(expression, m)`|Generates a non-fatal failure if the value of `expression` doesn't match matcher `m`. |
# Actions #
**Actions** specify what a mock function should do when invoked.
## Returning a Value ##
|`Return()`|Return from a `void` mock function.|
|:---------|:----------------------------------|
|`Return(value)`|Return `value`. If the type of `value` is different to the mock function's return type, `value` is converted to the latter type <i>at the time the expectation is set</i>, not when the action is executed.|
|`ReturnArg<N>()`|Return the `N`-th (0-based) argument.|
|`ReturnNew<T>(a1, ..., ak)`|Return `new T(a1, ..., ak)`; a different object is created each time.|
|`ReturnNull()`|Return a null pointer. |
|`ReturnPointee(ptr)`|Return the value pointed to by `ptr`.|
|`ReturnRef(variable)`|Return a reference to `variable`. |
|`ReturnRefOfCopy(value)`|Return a reference to a copy of `value`; the copy lives as long as the action.|
## Side Effects ##
|`Assign(&variable, value)`|Assign `value` to variable.|
|:-------------------------|:--------------------------|
| `DeleteArg<N>()` | Delete the `N`-th (0-based) argument, which must be a pointer. |
| `SaveArg<N>(pointer)` | Save the `N`-th (0-based) argument to `*pointer`. |
| `SaveArgPointee<N>(pointer)` | Save the value pointed to by the `N`-th (0-based) argument to `*pointer`. |
| `SetArgReferee<N>(value)` | Assign value to the variable referenced by the `N`-th (0-based) argument. |
|`SetArgPointee<N>(value)` |Assign `value` to the variable pointed by the `N`-th (0-based) argument.|
|`SetArgumentPointee<N>(value)`|Same as `SetArgPointee<N>(value)`. Deprecated. Will be removed in v1.7.0.|
|`SetArrayArgument<N>(first, last)`|Copies the elements in source range [`first`, `last`) to the array pointed to by the `N`-th (0-based) argument, which can be either a pointer or an iterator. The action does not take ownership of the elements in the source range.|
|`SetErrnoAndReturn(error, value)`|Set `errno` to `error` and return `value`.|
|`Throw(exception)` |Throws the given exception, which can be any copyable value. Available since v1.1.0.|
## Using a Function or a Functor as an Action ##
|`Invoke(f)`|Invoke `f` with the arguments passed to the mock function, where `f` can be a global/static function or a functor.|
|:----------|:-----------------------------------------------------------------------------------------------------------------|
|`Invoke(object_pointer, &class::method)`|Invoke the {method on the object with the arguments passed to the mock function. |
|`InvokeWithoutArgs(f)`|Invoke `f`, which can be a global/static function or a functor. `f` must take no arguments. |
|`InvokeWithoutArgs(object_pointer, &class::method)`|Invoke the method on the object, which takes no arguments. |
|`InvokeArgument<N>(arg1, arg2, ..., argk)`|Invoke the mock function's `N`-th (0-based) argument, which must be a function or a functor, with the `k` arguments.|
The return value of the invoked function is used as the return value
of the action.
When defining a function or functor to be used with `Invoke*()`, you can declare any unused parameters as `Unused`:
```
double Distance(Unused, double x, double y) { return sqrt(x*x + y*y); }
...
EXPECT_CALL(mock, Foo("Hi", _, _)).WillOnce(Invoke(Distance));
```
In `InvokeArgument<N>(...)`, if an argument needs to be passed by reference, wrap it inside `ByRef()`. For example,
```
InvokeArgument<2>(5, string("Hi"), ByRef(foo))
```
calls the mock function's #2 argument, passing to it `5` and `string("Hi")` by value, and `foo` by reference.
## Default Action ##
|`DoDefault()`|Do the default action (specified by `ON_CALL()` or the built-in one).|
|:------------|:--------------------------------------------------------------------|
**Note:** due to technical reasons, `DoDefault()` cannot be used inside a composite action - trying to do so will result in a run-time error.
## Composite Actions ##
|`DoAll(a1, a2, ..., an)`|Do all actions `a1` to `an` and return the result of `an` in each invocation. The first `n - 1` sub-actions must return void. |
|:-----------------------|:-----------------------------------------------------------------------------------------------------------------------------|
|`IgnoreResult(a)` |Perform action `a` and ignore its result. `a` must not return void. |
|`WithArg<N>(a)` |Pass the `N`-th (0-based) argument of the mock function to action `a` and perform it. |
|`WithArgs<N1, N2, ..., Nk>(a)`|Pass the selected (0-based) arguments of the mock function to action `a` and perform it. |
|`WithoutArgs(a)` |Perform action `a` without any arguments. |
## Defining Actions ##
| `ACTION(Sum) { return arg0 + arg1; }` | Defines an action `Sum()` to return the sum of the mock function's argument #0 and #1. |
|:--------------------------------------|:---------------------------------------------------------------------------------------|
| `ACTION_P(Plus, n) { return arg0 + n; }` | Defines an action `Plus(n)` to return the sum of the mock function's argument #0 and `n`. |
| `ACTION_Pk(Foo, p1, ..., pk) { statements; }` | Defines a parameterized action `Foo(p1, ..., pk)` to execute the given `statements`. |
The `ACTION*` macros cannot be used inside a function or class.
# Cardinalities #
These are used in `Times()` to specify how many times a mock function will be called:
|`AnyNumber()`|The function can be called any number of times.|
|:------------|:----------------------------------------------|
|`AtLeast(n)` |The call is expected at least `n` times. |
|`AtMost(n)` |The call is expected at most `n` times. |
|`Between(m, n)`|The call is expected between `m` and `n` (inclusive) times.|
|`Exactly(n) or n`|The call is expected exactly `n` times. In particular, the call should never happen when `n` is 0.|
# Expectation Order #
By default, the expectations can be matched in _any_ order. If some
or all expectations must be matched in a given order, there are two
ways to specify it. They can be used either independently or
together.
## The After Clause ##
```
using ::testing::Expectation;
...
Expectation init_x = EXPECT_CALL(foo, InitX());
Expectation init_y = EXPECT_CALL(foo, InitY());
EXPECT_CALL(foo, Bar())
.After(init_x, init_y);
```
says that `Bar()` can be called only after both `InitX()` and
`InitY()` have been called.
If you don't know how many pre-requisites an expectation has when you
write it, you can use an `ExpectationSet` to collect them:
```
using ::testing::ExpectationSet;
...
ExpectationSet all_inits;
for (int i = 0; i < element_count; i++) {
all_inits += EXPECT_CALL(foo, InitElement(i));
}
EXPECT_CALL(foo, Bar())
.After(all_inits);
```
says that `Bar()` can be called only after all elements have been
initialized (but we don't care about which elements get initialized
before the others).
Modifying an `ExpectationSet` after using it in an `.After()` doesn't
affect the meaning of the `.After()`.
## Sequences ##
When you have a long chain of sequential expectations, it's easier to
specify the order using **sequences**, which don't require you to given
each expectation in the chain a different name. <i>All expected<br>
calls</i> in the same sequence must occur in the order they are
specified.
```
using ::testing::Sequence;
Sequence s1, s2;
...
EXPECT_CALL(foo, Reset())
.InSequence(s1, s2)
.WillOnce(Return(true));
EXPECT_CALL(foo, GetSize())
.InSequence(s1)
.WillOnce(Return(1));
EXPECT_CALL(foo, Describe(A<const char*>()))
.InSequence(s2)
.WillOnce(Return("dummy"));
```
says that `Reset()` must be called before _both_ `GetSize()` _and_
`Describe()`, and the latter two can occur in any order.
To put many expectations in a sequence conveniently:
```
using ::testing::InSequence;
{
InSequence dummy;
EXPECT_CALL(...)...;
EXPECT_CALL(...)...;
...
EXPECT_CALL(...)...;
}
```
says that all expected calls in the scope of `dummy` must occur in
strict order. The name `dummy` is irrelevant.)
# Verifying and Resetting a Mock #
Google Mock will verify the expectations on a mock object when it is destructed, or you can do it earlier:
```
using ::testing::Mock;
...
// Verifies and removes the expectations on mock_obj;
// returns true iff successful.
Mock::VerifyAndClearExpectations(&mock_obj);
...
// Verifies and removes the expectations on mock_obj;
// also removes the default actions set by ON_CALL();
// returns true iff successful.
Mock::VerifyAndClear(&mock_obj);
```
You can also tell Google Mock that a mock object can be leaked and doesn't
need to be verified:
```
Mock::AllowLeak(&mock_obj);
```
# Mock Classes #
Google Mock defines a convenient mock class template
```
class MockFunction<R(A1, ..., An)> {
public:
MOCK_METHODn(Call, R(A1, ..., An));
};
```
See this [recipe](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Using_Check_Points) for one application of it.
# Flags #
| `--gmock_catch_leaked_mocks=0` | Don't report leaked mock objects as failures. |
|:-------------------------------|:----------------------------------------------|
| `--gmock_verbose=LEVEL` | Sets the default verbosity level (`info`, `warning`, or `error`) of Google Mock messages. |

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This page lists all documentation wiki pages for Google Mock **(the SVN trunk version)**
- **if you use a released version of Google Mock, please read the documentation for that specific version instead.**
* [ForDummies](V1_7_ForDummies.md) -- start here if you are new to Google Mock.
* [CheatSheet](V1_7_CheatSheet.md) -- a quick reference.
* [CookBook](V1_7_CookBook.md) -- recipes for doing various tasks using Google Mock.
* [FrequentlyAskedQuestions](V1_7_FrequentlyAskedQuestions.md) -- check here before asking a question on the mailing list.
To contribute code to Google Mock, read:
* [DevGuide](DevGuide.md) -- read this _before_ writing your first patch.
* [Pump Manual](http://code.google.com/p/googletest/wiki/PumpManual) -- how we generate some of Google Mock's source files.

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(**Note:** If you get compiler errors that you don't understand, be sure to consult [Google Mock Doctor](http://code.google.com/p/googlemock/wiki/V1_7_FrequentlyAskedQuestions#How_am_I_supposed_to_make_sense_of_these_horrible_template_error).)
# What Is Google C++ Mocking Framework? #
When you write a prototype or test, often it's not feasible or wise to rely on real objects entirely. A **mock object** implements the same interface as a real object (so it can be used as one), but lets you specify at run time how it will be used and what it should do (which methods will be called? in which order? how many times? with what arguments? what will they return? etc).
**Note:** It is easy to confuse the term _fake objects_ with mock objects. Fakes and mocks actually mean very different things in the Test-Driven Development (TDD) community:
* **Fake** objects have working implementations, but usually take some shortcut (perhaps to make the operations less expensive), which makes them not suitable for production. An in-memory file system would be an example of a fake.
* **Mocks** are objects pre-programmed with _expectations_, which form a specification of the calls they are expected to receive.
If all this seems too abstract for you, don't worry - the most important thing to remember is that a mock allows you to check the _interaction_ between itself and code that uses it. The difference between fakes and mocks will become much clearer once you start to use mocks.
**Google C++ Mocking Framework** (or **Google Mock** for short) is a library (sometimes we also call it a "framework" to make it sound cool) for creating mock classes and using them. It does to C++ what [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/) do to Java.
Using Google Mock involves three basic steps:
1. Use some simple macros to describe the interface you want to mock, and they will expand to the implementation of your mock class;
1. Create some mock objects and specify its expectations and behavior using an intuitive syntax;
1. Exercise code that uses the mock objects. Google Mock will catch any violation of the expectations as soon as it arises.
# Why Google Mock? #
While mock objects help you remove unnecessary dependencies in tests and make them fast and reliable, using mocks manually in C++ is _hard_:
* Someone has to implement the mocks. The job is usually tedious and error-prone. No wonder people go great distance to avoid it.
* The quality of those manually written mocks is a bit, uh, unpredictable. You may see some really polished ones, but you may also see some that were hacked up in a hurry and have all sorts of ad hoc restrictions.
* The knowledge you gained from using one mock doesn't transfer to the next.
In contrast, Java and Python programmers have some fine mock frameworks, which automate the creation of mocks. As a result, mocking is a proven effective technique and widely adopted practice in those communities. Having the right tool absolutely makes the difference.
Google Mock was built to help C++ programmers. It was inspired by [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/), but designed with C++'s specifics in mind. It is your friend if any of the following problems is bothering you:
* You are stuck with a sub-optimal design and wish you had done more prototyping before it was too late, but prototyping in C++ is by no means "rapid".
* Your tests are slow as they depend on too many libraries or use expensive resources (e.g. a database).
* Your tests are brittle as some resources they use are unreliable (e.g. the network).
* You want to test how your code handles a failure (e.g. a file checksum error), but it's not easy to cause one.
* You need to make sure that your module interacts with other modules in the right way, but it's hard to observe the interaction; therefore you resort to observing the side effects at the end of the action, which is awkward at best.
* You want to "mock out" your dependencies, except that they don't have mock implementations yet; and, frankly, you aren't thrilled by some of those hand-written mocks.
We encourage you to use Google Mock as:
* a _design_ tool, for it lets you experiment with your interface design early and often. More iterations lead to better designs!
* a _testing_ tool to cut your tests' outbound dependencies and probe the interaction between your module and its collaborators.
# Getting Started #
Using Google Mock is easy! Inside your C++ source file, just `#include` `"gtest/gtest.h"` and `"gmock/gmock.h"`, and you are ready to go.
# A Case for Mock Turtles #
Let's look at an example. Suppose you are developing a graphics program that relies on a LOGO-like API for drawing. How would you test that it does the right thing? Well, you can run it and compare the screen with a golden screen snapshot, but let's admit it: tests like this are expensive to run and fragile (What if you just upgraded to a shiny new graphics card that has better anti-aliasing? Suddenly you have to update all your golden images.). It would be too painful if all your tests are like this. Fortunately, you learned about Dependency Injection and know the right thing to do: instead of having your application talk to the drawing API directly, wrap the API in an interface (say, `Turtle`) and code to that interface:
```
class Turtle {
...
virtual ~Turtle() {}
virtual void PenUp() = 0;
virtual void PenDown() = 0;
virtual void Forward(int distance) = 0;
virtual void Turn(int degrees) = 0;
virtual void GoTo(int x, int y) = 0;
virtual int GetX() const = 0;
virtual int GetY() const = 0;
};
```
(Note that the destructor of `Turtle` **must** be virtual, as is the case for **all** classes you intend to inherit from - otherwise the destructor of the derived class will not be called when you delete an object through a base pointer, and you'll get corrupted program states like memory leaks.)
You can control whether the turtle's movement will leave a trace using `PenUp()` and `PenDown()`, and control its movement using `Forward()`, `Turn()`, and `GoTo()`. Finally, `GetX()` and `GetY()` tell you the current position of the turtle.
Your program will normally use a real implementation of this interface. In tests, you can use a mock implementation instead. This allows you to easily check what drawing primitives your program is calling, with what arguments, and in which order. Tests written this way are much more robust (they won't break because your new machine does anti-aliasing differently), easier to read and maintain (the intent of a test is expressed in the code, not in some binary images), and run _much, much faster_.
# Writing the Mock Class #
If you are lucky, the mocks you need to use have already been implemented by some nice people. If, however, you find yourself in the position to write a mock class, relax - Google Mock turns this task into a fun game! (Well, almost.)
## How to Define It ##
Using the `Turtle` interface as example, here are the simple steps you need to follow:
1. Derive a class `MockTurtle` from `Turtle`.
1. Take a _virtual_ function of `Turtle` (while it's possible to [mock non-virtual methods using templates](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Mocking_Nonvirtual_Methods), it's much more involved). Count how many arguments it has.
1. In the `public:` section of the child class, write `MOCK_METHODn();` (or `MOCK_CONST_METHODn();` if you are mocking a `const` method), where `n` is the number of the arguments; if you counted wrong, shame on you, and a compiler error will tell you so.
1. Now comes the fun part: you take the function signature, cut-and-paste the _function name_ as the _first_ argument to the macro, and leave what's left as the _second_ argument (in case you're curious, this is the _type of the function_).
1. Repeat until all virtual functions you want to mock are done.
After the process, you should have something like:
```
#include "gmock/gmock.h" // Brings in Google Mock.
class MockTurtle : public Turtle {
public:
...
MOCK_METHOD0(PenUp, void());
MOCK_METHOD0(PenDown, void());
MOCK_METHOD1(Forward, void(int distance));
MOCK_METHOD1(Turn, void(int degrees));
MOCK_METHOD2(GoTo, void(int x, int y));
MOCK_CONST_METHOD0(GetX, int());
MOCK_CONST_METHOD0(GetY, int());
};
```
You don't need to define these mock methods somewhere else - the `MOCK_METHOD*` macros will generate the definitions for you. It's that simple! Once you get the hang of it, you can pump out mock classes faster than your source-control system can handle your check-ins.
**Tip:** If even this is too much work for you, you'll find the
`gmock_gen.py` tool in Google Mock's `scripts/generator/` directory (courtesy of the [cppclean](http://code.google.com/p/cppclean/) project) useful. This command-line
tool requires that you have Python 2.4 installed. You give it a C++ file and the name of an abstract class defined in it,
and it will print the definition of the mock class for you. Due to the
complexity of the C++ language, this script may not always work, but
it can be quite handy when it does. For more details, read the [user documentation](http://code.google.com/p/googlemock/source/browse/trunk/scripts/generator/README).
## Where to Put It ##
When you define a mock class, you need to decide where to put its definition. Some people put it in a `*_test.cc`. This is fine when the interface being mocked (say, `Foo`) is owned by the same person or team. Otherwise, when the owner of `Foo` changes it, your test could break. (You can't really expect `Foo`'s maintainer to fix every test that uses `Foo`, can you?)
So, the rule of thumb is: if you need to mock `Foo` and it's owned by others, define the mock class in `Foo`'s package (better, in a `testing` sub-package such that you can clearly separate production code and testing utilities), and put it in a `mock_foo.h`. Then everyone can reference `mock_foo.h` from their tests. If `Foo` ever changes, there is only one copy of `MockFoo` to change, and only tests that depend on the changed methods need to be fixed.
Another way to do it: you can introduce a thin layer `FooAdaptor` on top of `Foo` and code to this new interface. Since you own `FooAdaptor`, you can absorb changes in `Foo` much more easily. While this is more work initially, carefully choosing the adaptor interface can make your code easier to write and more readable (a net win in the long run), as you can choose `FooAdaptor` to fit your specific domain much better than `Foo` does.
# Using Mocks in Tests #
Once you have a mock class, using it is easy. The typical work flow is:
1. Import the Google Mock names from the `testing` namespace such that you can use them unqualified (You only have to do it once per file. Remember that namespaces are a good idea and good for your health.).
1. Create some mock objects.
1. Specify your expectations on them (How many times will a method be called? With what arguments? What should it do? etc.).
1. Exercise some code that uses the mocks; optionally, check the result using Google Test assertions. If a mock method is called more than expected or with wrong arguments, you'll get an error immediately.
1. When a mock is destructed, Google Mock will automatically check whether all expectations on it have been satisfied.
Here's an example:
```
#include "path/to/mock-turtle.h"
#include "gmock/gmock.h"
#include "gtest/gtest.h"
using ::testing::AtLeast; // #1
TEST(PainterTest, CanDrawSomething) {
MockTurtle turtle; // #2
EXPECT_CALL(turtle, PenDown()) // #3
.Times(AtLeast(1));
Painter painter(&turtle); // #4
EXPECT_TRUE(painter.DrawCircle(0, 0, 10));
} // #5
int main(int argc, char** argv) {
// The following line must be executed to initialize Google Mock
// (and Google Test) before running the tests.
::testing::InitGoogleMock(&argc, argv);
return RUN_ALL_TESTS();
}
```
As you might have guessed, this test checks that `PenDown()` is called at least once. If the `painter` object didn't call this method, your test will fail with a message like this:
```
path/to/my_test.cc:119: Failure
Actual function call count doesn't match this expectation:
Actually: never called;
Expected: called at least once.
```
**Tip 1:** If you run the test from an Emacs buffer, you can hit `<Enter>` on the line number displayed in the error message to jump right to the failed expectation.
**Tip 2:** If your mock objects are never deleted, the final verification won't happen. Therefore it's a good idea to use a heap leak checker in your tests when you allocate mocks on the heap.
**Important note:** Google Mock requires expectations to be set **before** the mock functions are called, otherwise the behavior is **undefined**. In particular, you mustn't interleave `EXPECT_CALL()`s and calls to the mock functions.
This means `EXPECT_CALL()` should be read as expecting that a call will occur _in the future_, not that a call has occurred. Why does Google Mock work like that? Well, specifying the expectation beforehand allows Google Mock to report a violation as soon as it arises, when the context (stack trace, etc) is still available. This makes debugging much easier.
Admittedly, this test is contrived and doesn't do much. You can easily achieve the same effect without using Google Mock. However, as we shall reveal soon, Google Mock allows you to do _much more_ with the mocks.
## Using Google Mock with Any Testing Framework ##
If you want to use something other than Google Test (e.g. [CppUnit](http://apps.sourceforge.net/mediawiki/cppunit/index.php?title=Main_Page) or
[CxxTest](http://cxxtest.tigris.org/)) as your testing framework, just change the `main()` function in the previous section to:
```
int main(int argc, char** argv) {
// The following line causes Google Mock to throw an exception on failure,
// which will be interpreted by your testing framework as a test failure.
::testing::GTEST_FLAG(throw_on_failure) = true;
::testing::InitGoogleMock(&argc, argv);
... whatever your testing framework requires ...
}
```
This approach has a catch: it makes Google Mock throw an exception
from a mock object's destructor sometimes. With some compilers, this
sometimes causes the test program to crash. You'll still be able to
notice that the test has failed, but it's not a graceful failure.
A better solution is to use Google Test's
[event listener API](http://code.google.com/p/googletest/wiki/AdvancedGuide#Extending_Google_Test_by_Handling_Test_Events)
to report a test failure to your testing framework properly. You'll need to
implement the `OnTestPartResult()` method of the event listener interface, but it
should be straightforward.
If this turns out to be too much work, we suggest that you stick with
Google Test, which works with Google Mock seamlessly (in fact, it is
technically part of Google Mock.). If there is a reason that you
cannot use Google Test, please let us know.
# Setting Expectations #
The key to using a mock object successfully is to set the _right expectations_ on it. If you set the expectations too strict, your test will fail as the result of unrelated changes. If you set them too loose, bugs can slip through. You want to do it just right such that your test can catch exactly the kind of bugs you intend it to catch. Google Mock provides the necessary means for you to do it "just right."
## General Syntax ##
In Google Mock we use the `EXPECT_CALL()` macro to set an expectation on a mock method. The general syntax is:
```
EXPECT_CALL(mock_object, method(matchers))
.Times(cardinality)
.WillOnce(action)
.WillRepeatedly(action);
```
The macro has two arguments: first the mock object, and then the method and its arguments. Note that the two are separated by a comma (`,`), not a period (`.`). (Why using a comma? The answer is that it was necessary for technical reasons.)
The macro can be followed by some optional _clauses_ that provide more information about the expectation. We'll discuss how each clause works in the coming sections.
This syntax is designed to make an expectation read like English. For example, you can probably guess that
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetX())
.Times(5)
.WillOnce(Return(100))
.WillOnce(Return(150))
.WillRepeatedly(Return(200));
```
says that the `turtle` object's `GetX()` method will be called five times, it will return 100 the first time, 150 the second time, and then 200 every time. Some people like to call this style of syntax a Domain-Specific Language (DSL).
**Note:** Why do we use a macro to do this? It serves two purposes: first it makes expectations easily identifiable (either by `grep` or by a human reader), and second it allows Google Mock to include the source file location of a failed expectation in messages, making debugging easier.
## Matchers: What Arguments Do We Expect? ##
When a mock function takes arguments, we must specify what arguments we are expecting; for example:
```
// Expects the turtle to move forward by 100 units.
EXPECT_CALL(turtle, Forward(100));
```
Sometimes you may not want to be too specific (Remember that talk about tests being too rigid? Over specification leads to brittle tests and obscures the intent of tests. Therefore we encourage you to specify only what's necessary - no more, no less.). If you care to check that `Forward()` will be called but aren't interested in its actual argument, write `_` as the argument, which means "anything goes":
```
using ::testing::_;
...
// Expects the turtle to move forward.
EXPECT_CALL(turtle, Forward(_));
```
`_` is an instance of what we call **matchers**. A matcher is like a predicate and can test whether an argument is what we'd expect. You can use a matcher inside `EXPECT_CALL()` wherever a function argument is expected.
A list of built-in matchers can be found in the [CheatSheet](V1_7_CheatSheet.md). For example, here's the `Ge` (greater than or equal) matcher:
```
using ::testing::Ge;...
EXPECT_CALL(turtle, Forward(Ge(100)));
```
This checks that the turtle will be told to go forward by at least 100 units.
## Cardinalities: How Many Times Will It Be Called? ##
The first clause we can specify following an `EXPECT_CALL()` is `Times()`. We call its argument a **cardinality** as it tells _how many times_ the call should occur. It allows us to repeat an expectation many times without actually writing it as many times. More importantly, a cardinality can be "fuzzy", just like a matcher can be. This allows a user to express the intent of a test exactly.
An interesting special case is when we say `Times(0)`. You may have guessed - it means that the function shouldn't be called with the given arguments at all, and Google Mock will report a Google Test failure whenever the function is (wrongfully) called.
We've seen `AtLeast(n)` as an example of fuzzy cardinalities earlier. For the list of built-in cardinalities you can use, see the [CheatSheet](V1_7_CheatSheet.md).
The `Times()` clause can be omitted. **If you omit `Times()`, Google Mock will infer the cardinality for you.** The rules are easy to remember:
* If **neither** `WillOnce()` **nor** `WillRepeatedly()` is in the `EXPECT_CALL()`, the inferred cardinality is `Times(1)`.
* If there are `n WillOnce()`'s but **no** `WillRepeatedly()`, where `n` >= 1, the cardinality is `Times(n)`.
* If there are `n WillOnce()`'s and **one** `WillRepeatedly()`, where `n` >= 0, the cardinality is `Times(AtLeast(n))`.
**Quick quiz:** what do you think will happen if a function is expected to be called twice but actually called four times?
## Actions: What Should It Do? ##
Remember that a mock object doesn't really have a working implementation? We as users have to tell it what to do when a method is invoked. This is easy in Google Mock.
First, if the return type of a mock function is a built-in type or a pointer, the function has a **default action** (a `void` function will just return, a `bool` function will return `false`, and other functions will return 0). If you don't say anything, this behavior will be used.
Second, if a mock function doesn't have a default action, or the default action doesn't suit you, you can specify the action to be taken each time the expectation matches using a series of `WillOnce()` clauses followed by an optional `WillRepeatedly()`. For example,
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillOnce(Return(300));
```
This says that `turtle.GetX()` will be called _exactly three times_ (Google Mock inferred this from how many `WillOnce()` clauses we've written, since we didn't explicitly write `Times()`), and will return 100, 200, and 300 respectively.
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetY())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillRepeatedly(Return(300));
```
says that `turtle.GetY()` will be called _at least twice_ (Google Mock knows this as we've written two `WillOnce()` clauses and a `WillRepeatedly()` while having no explicit `Times()`), will return 100 the first time, 200 the second time, and 300 from the third time on.
Of course, if you explicitly write a `Times()`, Google Mock will not try to infer the cardinality itself. What if the number you specified is larger than there are `WillOnce()` clauses? Well, after all `WillOnce()`s are used up, Google Mock will do the _default_ action for the function every time (unless, of course, you have a `WillRepeatedly()`.).
What can we do inside `WillOnce()` besides `Return()`? You can return a reference using `ReturnRef(variable)`, or invoke a pre-defined function, among [others](http://code.google.com/p/googlemock/wiki/V1_7_CheatSheet#Actions).
**Important note:** The `EXPECT_CALL()` statement evaluates the action clause only once, even though the action may be performed many times. Therefore you must be careful about side effects. The following may not do what you want:
```
int n = 100;
EXPECT_CALL(turtle, GetX())
.Times(4)
.WillRepeatedly(Return(n++));
```
Instead of returning 100, 101, 102, ..., consecutively, this mock function will always return 100 as `n++` is only evaluated once. Similarly, `Return(new Foo)` will create a new `Foo` object when the `EXPECT_CALL()` is executed, and will return the same pointer every time. If you want the side effect to happen every time, you need to define a custom action, which we'll teach in the [CookBook](V1_7_CookBook.md).
Time for another quiz! What do you think the following means?
```
using ::testing::Return;...
EXPECT_CALL(turtle, GetY())
.Times(4)
.WillOnce(Return(100));
```
Obviously `turtle.GetY()` is expected to be called four times. But if you think it will return 100 every time, think twice! Remember that one `WillOnce()` clause will be consumed each time the function is invoked and the default action will be taken afterwards. So the right answer is that `turtle.GetY()` will return 100 the first time, but **return 0 from the second time on**, as returning 0 is the default action for `int` functions.
## Using Multiple Expectations ##
So far we've only shown examples where you have a single expectation. More realistically, you're going to specify expectations on multiple mock methods, which may be from multiple mock objects.
By default, when a mock method is invoked, Google Mock will search the expectations in the **reverse order** they are defined, and stop when an active expectation that matches the arguments is found (you can think of it as "newer rules override older ones."). If the matching expectation cannot take any more calls, you will get an upper-bound-violated failure. Here's an example:
```
using ::testing::_;...
EXPECT_CALL(turtle, Forward(_)); // #1
EXPECT_CALL(turtle, Forward(10)) // #2
.Times(2);
```
If `Forward(10)` is called three times in a row, the third time it will be an error, as the last matching expectation (#2) has been saturated. If, however, the third `Forward(10)` call is replaced by `Forward(20)`, then it would be OK, as now #1 will be the matching expectation.
**Side note:** Why does Google Mock search for a match in the _reverse_ order of the expectations? The reason is that this allows a user to set up the default expectations in a mock object's constructor or the test fixture's set-up phase and then customize the mock by writing more specific expectations in the test body. So, if you have two expectations on the same method, you want to put the one with more specific matchers **after** the other, or the more specific rule would be shadowed by the more general one that comes after it.
## Ordered vs Unordered Calls ##
By default, an expectation can match a call even though an earlier expectation hasn't been satisfied. In other words, the calls don't have to occur in the order the expectations are specified.
Sometimes, you may want all the expected calls to occur in a strict order. To say this in Google Mock is easy:
```
using ::testing::InSequence;...
TEST(FooTest, DrawsLineSegment) {
...
{
InSequence dummy;
EXPECT_CALL(turtle, PenDown());
EXPECT_CALL(turtle, Forward(100));
EXPECT_CALL(turtle, PenUp());
}
Foo();
}
```
By creating an object of type `InSequence`, all expectations in its scope are put into a _sequence_ and have to occur _sequentially_. Since we are just relying on the constructor and destructor of this object to do the actual work, its name is really irrelevant.
In this example, we test that `Foo()` calls the three expected functions in the order as written. If a call is made out-of-order, it will be an error.
(What if you care about the relative order of some of the calls, but not all of them? Can you specify an arbitrary partial order? The answer is ... yes! If you are impatient, the details can be found in the [CookBook](V1_7_CookBook#Expecting_Partially_Ordered_Calls.md).)
## All Expectations Are Sticky (Unless Said Otherwise) ##
Now let's do a quick quiz to see how well you can use this mock stuff already. How would you test that the turtle is asked to go to the origin _exactly twice_ (you want to ignore any other instructions it receives)?
After you've come up with your answer, take a look at ours and compare notes (solve it yourself first - don't cheat!):
```
using ::testing::_;...
EXPECT_CALL(turtle, GoTo(_, _)) // #1
.Times(AnyNumber());
EXPECT_CALL(turtle, GoTo(0, 0)) // #2
.Times(2);
```
Suppose `turtle.GoTo(0, 0)` is called three times. In the third time, Google Mock will see that the arguments match expectation #2 (remember that we always pick the last matching expectation). Now, since we said that there should be only two such calls, Google Mock will report an error immediately. This is basically what we've told you in the "Using Multiple Expectations" section above.
This example shows that **expectations in Google Mock are "sticky" by default**, in the sense that they remain active even after we have reached their invocation upper bounds. This is an important rule to remember, as it affects the meaning of the spec, and is **different** to how it's done in many other mocking frameworks (Why'd we do that? Because we think our rule makes the common cases easier to express and understand.).
Simple? Let's see if you've really understood it: what does the following code say?
```
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i));
}
```
If you think it says that `turtle.GetX()` will be called `n` times and will return 10, 20, 30, ..., consecutively, think twice! The problem is that, as we said, expectations are sticky. So, the second time `turtle.GetX()` is called, the last (latest) `EXPECT_CALL()` statement will match, and will immediately lead to an "upper bound exceeded" error - this piece of code is not very useful!
One correct way of saying that `turtle.GetX()` will return 10, 20, 30, ..., is to explicitly say that the expectations are _not_ sticky. In other words, they should _retire_ as soon as they are saturated:
```
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
```
And, there's a better way to do it: in this case, we expect the calls to occur in a specific order, and we line up the actions to match the order. Since the order is important here, we should make it explicit using a sequence:
```
using ::testing::InSequence;
using ::testing::Return;
...
{
InSequence s;
for (int i = 1; i <= n; i++) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
}
```
By the way, the other situation where an expectation may _not_ be sticky is when it's in a sequence - as soon as another expectation that comes after it in the sequence has been used, it automatically retires (and will never be used to match any call).
## Uninteresting Calls ##
A mock object may have many methods, and not all of them are that interesting. For example, in some tests we may not care about how many times `GetX()` and `GetY()` get called.
In Google Mock, if you are not interested in a method, just don't say anything about it. If a call to this method occurs, you'll see a warning in the test output, but it won't be a failure.
# What Now? #
Congratulations! You've learned enough about Google Mock to start using it. Now, you might want to join the [googlemock](http://groups.google.com/group/googlemock) discussion group and actually write some tests using Google Mock - it will be fun. Hey, it may even be addictive - you've been warned.
Then, if you feel like increasing your mock quotient, you should move on to the [CookBook](V1_7_CookBook.md). You can learn many advanced features of Google Mock there -- and advance your level of enjoyment and testing bliss.

628
googlemock/docs/v1_7/FrequentlyAskedQuestions.md
Unescape View File

@ -1,628 +0,0 @@
Please send your questions to the
[googlemock](http://groups.google.com/group/googlemock) discussion
group. If you need help with compiler errors, make sure you have
tried [Google Mock Doctor](#How_am_I_supposed_to_make_sense_of_these_horrible_template_error.md) first.
## When I call a method on my mock object, the method for the real object is invoked instead. What's the problem? ##
In order for a method to be mocked, it must be _virtual_, unless you use the [high-perf dependency injection technique](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Mocking_Nonvirtual_Methods).
## I wrote some matchers. After I upgraded to a new version of Google Mock, they no longer compile. What's going on? ##
After version 1.4.0 of Google Mock was released, we had an idea on how
to make it easier to write matchers that can generate informative
messages efficiently. We experimented with this idea and liked what
we saw. Therefore we decided to implement it.
Unfortunately, this means that if you have defined your own matchers
by implementing `MatcherInterface` or using `MakePolymorphicMatcher()`,
your definitions will no longer compile. Matchers defined using the
`MATCHER*` family of macros are not affected.
Sorry for the hassle if your matchers are affected. We believe it's
in everyone's long-term interest to make this change sooner than
later. Fortunately, it's usually not hard to migrate an existing
matcher to the new API. Here's what you need to do:
If you wrote your matcher like this:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
you'll need to change it to:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
(i.e. rename `Matches()` to `MatchAndExplain()` and give it a second
argument of type `MatchResultListener*`.)
If you were also using `ExplainMatchResultTo()` to improve the matcher
message:
```
// Old matcher definition that doesn't work with the lastest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
virtual void ExplainMatchResultTo(MyType value,
::std::ostream* os) const {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Foo property is " << value.GetFoo();
}
...
};
```
you should move the logic of `ExplainMatchResultTo()` into
`MatchAndExplain()`, using the `MatchResultListener` argument where
the `::std::ostream` was used:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Foo property is " << value.GetFoo();
return value.GetFoo() > 5;
}
...
};
```
If your matcher is defined using `MakePolymorphicMatcher()`:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you should rename the `Matches()` method to `MatchAndExplain()` and
add a `MatchResultListener*` argument (the same as what you need to do
for matchers defined by implementing `MatcherInterface`):
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
If your polymorphic matcher uses `ExplainMatchResultTo()` for better
failure messages:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
void ExplainMatchResultTo(const MyGreatMatcher& matcher,
MyType value,
::std::ostream* os) {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Bar property is " << value.GetBar();
}
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you'll need to move the logic inside `ExplainMatchResultTo()` to
`MatchAndExplain()`:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Bar property is " << value.GetBar();
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
For more information, you can read these
[two](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Writing_New_Monomorphic_Matchers)
[recipes](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Writing_New_Polymorphic_Matchers)
from the cookbook. As always, you
are welcome to post questions on `googlemock@googlegroups.com` if you
need any help.
## When using Google Mock, do I have to use Google Test as the testing framework? I have my favorite testing framework and don't want to switch. ##
Google Mock works out of the box with Google Test. However, it's easy
to configure it to work with any testing framework of your choice.
[Here](http://code.google.com/p/googlemock/wiki/V1_7_ForDummies#Using_Google_Mock_with_Any_Testing_Framework) is how.
## How am I supposed to make sense of these horrible template errors? ##
If you are confused by the compiler errors gcc threw at you,
try consulting the _Google Mock Doctor_ tool first. What it does is to
scan stdin for gcc error messages, and spit out diagnoses on the
problems (we call them diseases) your code has.
To "install", run command:
```
alias gmd='<path to googlemock>/scripts/gmock_doctor.py'
```
To use it, do:
```
<your-favorite-build-command> <your-test> 2>&1 | gmd
```
For example:
```
make my_test 2>&1 | gmd
```
Or you can run `gmd` and copy-n-paste gcc's error messages to it.
## Can I mock a variadic function? ##
You cannot mock a variadic function (i.e. a function taking ellipsis
(`...`) arguments) directly in Google Mock.
The problem is that in general, there is _no way_ for a mock object to
know how many arguments are passed to the variadic method, and what
the arguments' types are. Only the _author of the base class_ knows
the protocol, and we cannot look into his head.
Therefore, to mock such a function, the _user_ must teach the mock
object how to figure out the number of arguments and their types. One
way to do it is to provide overloaded versions of the function.
Ellipsis arguments are inherited from C and not really a C++ feature.
They are unsafe to use and don't work with arguments that have
constructors or destructors. Therefore we recommend to avoid them in
C++ as much as possible.
## MSVC gives me warning C4301 or C4373 when I define a mock method with a const parameter. Why? ##
If you compile this using Microsoft Visual C++ 2005 SP1:
```
class Foo {
...
virtual void Bar(const int i) = 0;
};
class MockFoo : public Foo {
...
MOCK_METHOD1(Bar, void(const int i));
};
```
You may get the following warning:
```
warning C4301: 'MockFoo::Bar': overriding virtual function only differs from 'Foo::Bar' by const/volatile qualifier
```
This is a MSVC bug. The same code compiles fine with gcc ,for
example. If you use Visual C++ 2008 SP1, you would get the warning:
```
warning C4373: 'MockFoo::Bar': virtual function overrides 'Foo::Bar', previous versions of the compiler did not override when parameters only differed by const/volatile qualifiers
```
In C++, if you _declare_ a function with a `const` parameter, the
`const` modifier is _ignored_. Therefore, the `Foo` base class above
is equivalent to:
```
class Foo {
...
virtual void Bar(int i) = 0; // int or const int? Makes no difference.
};
```
In fact, you can _declare_ Bar() with an `int` parameter, and _define_
it with a `const int` parameter. The compiler will still match them
up.
Since making a parameter `const` is meaningless in the method
_declaration_, we recommend to remove it in both `Foo` and `MockFoo`.
That should workaround the VC bug.
Note that we are talking about the _top-level_ `const` modifier here.
If the function parameter is passed by pointer or reference, declaring
the _pointee_ or _referee_ as `const` is still meaningful. For
example, the following two declarations are _not_ equivalent:
```
void Bar(int* p); // Neither p nor *p is const.
void Bar(const int* p); // p is not const, but *p is.
```
## I have a huge mock class, and Microsoft Visual C++ runs out of memory when compiling it. What can I do? ##
We've noticed that when the `/clr` compiler flag is used, Visual C++
uses 5~6 times as much memory when compiling a mock class. We suggest
to avoid `/clr` when compiling native C++ mocks.
## I can't figure out why Google Mock thinks my expectations are not satisfied. What should I do? ##
You might want to run your test with
`--gmock_verbose=info`. This flag lets Google Mock print a trace
of every mock function call it receives. By studying the trace,
you'll gain insights on why the expectations you set are not met.
## How can I assert that a function is NEVER called? ##
```
EXPECT_CALL(foo, Bar(_))
.Times(0);
```
## I have a failed test where Google Mock tells me TWICE that a particular expectation is not satisfied. Isn't this redundant? ##
When Google Mock detects a failure, it prints relevant information
(the mock function arguments, the state of relevant expectations, and
etc) to help the user debug. If another failure is detected, Google
Mock will do the same, including printing the state of relevant
expectations.
Sometimes an expectation's state didn't change between two failures,
and you'll see the same description of the state twice. They are
however _not_ redundant, as they refer to _different points in time_.
The fact they are the same _is_ interesting information.
## I get a heap check failure when using a mock object, but using a real object is fine. What can be wrong? ##
Does the class (hopefully a pure interface) you are mocking have a
virtual destructor?
Whenever you derive from a base class, make sure its destructor is
virtual. Otherwise Bad Things will happen. Consider the following
code:
```
class Base {
public:
// Not virtual, but should be.
~Base() { ... }
...
};
class Derived : public Base {
public:
...
private:
std::string value_;
};
...
Base* p = new Derived;
...
delete p; // Surprise! ~Base() will be called, but ~Derived() will not
// - value_ is leaked.
```
By changing `~Base()` to virtual, `~Derived()` will be correctly
called when `delete p` is executed, and the heap checker
will be happy.
## The "newer expectations override older ones" rule makes writing expectations awkward. Why does Google Mock do that? ##
When people complain about this, often they are referring to code like:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. However, I have to write the expectations in the
// reverse order. This sucks big time!!!
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
```
The problem is that they didn't pick the **best** way to express the test's
intent.
By default, expectations don't have to be matched in _any_ particular
order. If you want them to match in a certain order, you need to be
explicit. This is Google Mock's (and jMock's) fundamental philosophy: it's
easy to accidentally over-specify your tests, and we want to make it
harder to do so.
There are two better ways to write the test spec. You could either
put the expectations in sequence:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. Using a sequence, we can write the expectations
// in their natural order.
{
InSequence s;
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
}
```
or you can put the sequence of actions in the same expectation:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time.
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.WillOnce(Return(2))
.RetiresOnSaturation();
```
Back to the original questions: why does Google Mock search the
expectations (and `ON_CALL`s) from back to front? Because this
allows a user to set up a mock's behavior for the common case early
(e.g. in the mock's constructor or the test fixture's set-up phase)
and customize it with more specific rules later. If Google Mock
searches from front to back, this very useful pattern won't be
possible.
## Google Mock prints a warning when a function without EXPECT\_CALL is called, even if I have set its behavior using ON\_CALL. Would it be reasonable not to show the warning in this case? ##
When choosing between being neat and being safe, we lean toward the
latter. So the answer is that we think it's better to show the
warning.
Often people write `ON_CALL`s in the mock object's
constructor or `SetUp()`, as the default behavior rarely changes from
test to test. Then in the test body they set the expectations, which
are often different for each test. Having an `ON_CALL` in the set-up
part of a test doesn't mean that the calls are expected. If there's
no `EXPECT_CALL` and the method is called, it's possibly an error. If
we quietly let the call go through without notifying the user, bugs
may creep in unnoticed.
If, however, you are sure that the calls are OK, you can write
```
EXPECT_CALL(foo, Bar(_))
.WillRepeatedly(...);
```
instead of
```
ON_CALL(foo, Bar(_))
.WillByDefault(...);
```
This tells Google Mock that you do expect the calls and no warning should be
printed.
Also, you can control the verbosity using the `--gmock_verbose` flag.
If you find the output too noisy when debugging, just choose a less
verbose level.
## How can I delete the mock function's argument in an action? ##
If you find yourself needing to perform some action that's not
supported by Google Mock directly, remember that you can define your own
actions using
[MakeAction()](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Writing_New_Actions) or
[MakePolymorphicAction()](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Writing_New_Polymorphic_Actions),
or you can write a stub function and invoke it using
[Invoke()](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Using_Functions_Methods_Functors).
## MOCK\_METHODn()'s second argument looks funny. Why don't you use the MOCK\_METHODn(Method, return\_type, arg\_1, ..., arg\_n) syntax? ##
What?! I think it's beautiful. :-)
While which syntax looks more natural is a subjective matter to some
extent, Google Mock's syntax was chosen for several practical advantages it
has.
Try to mock a function that takes a map as an argument:
```
virtual int GetSize(const map<int, std::string>& m);
```
Using the proposed syntax, it would be:
```
MOCK_METHOD1(GetSize, int, const map<int, std::string>& m);
```
Guess what? You'll get a compiler error as the compiler thinks that
`const map<int, std::string>& m` are **two**, not one, arguments. To work
around this you can use `typedef` to give the map type a name, but
that gets in the way of your work. Google Mock's syntax avoids this
problem as the function's argument types are protected inside a pair
of parentheses:
```
// This compiles fine.
MOCK_METHOD1(GetSize, int(const map<int, std::string>& m));
```
You still need a `typedef` if the return type contains an unprotected
comma, but that's much rarer.
Other advantages include:
1. `MOCK_METHOD1(Foo, int, bool)` can leave a reader wonder whether the method returns `int` or `bool`, while there won't be such confusion using Google Mock's syntax.
1. The way Google Mock describes a function type is nothing new, although many people may not be familiar with it. The same syntax was used in C, and the `function` library in `tr1` uses this syntax extensively. Since `tr1` will become a part of the new version of STL, we feel very comfortable to be consistent with it.
1. The function type syntax is also used in other parts of Google Mock's API (e.g. the action interface) in order to make the implementation tractable. A user needs to learn it anyway in order to utilize Google Mock's more advanced features. We'd as well stick to the same syntax in `MOCK_METHOD*`!
## My code calls a static/global function. Can I mock it? ##
You can, but you need to make some changes.
In general, if you find yourself needing to mock a static function,
it's a sign that your modules are too tightly coupled (and less
flexible, less reusable, less testable, etc). You are probably better
off defining a small interface and call the function through that
interface, which then can be easily mocked. It's a bit of work
initially, but usually pays for itself quickly.
This Google Testing Blog
[post](http://googletesting.blogspot.com/2008/06/defeat-static-cling.html)
says it excellently. Check it out.
## My mock object needs to do complex stuff. It's a lot of pain to specify the actions. Google Mock sucks! ##
I know it's not a question, but you get an answer for free any way. :-)
With Google Mock, you can create mocks in C++ easily. And people might be
tempted to use them everywhere. Sometimes they work great, and
sometimes you may find them, well, a pain to use. So, what's wrong in
the latter case?
When you write a test without using mocks, you exercise the code and
assert that it returns the correct value or that the system is in an
expected state. This is sometimes called "state-based testing".
Mocks are great for what some call "interaction-based" testing:
instead of checking the system state at the very end, mock objects
verify that they are invoked the right way and report an error as soon
as it arises, giving you a handle on the precise context in which the
error was triggered. This is often more effective and economical to
do than state-based testing.
If you are doing state-based testing and using a test double just to
simulate the real object, you are probably better off using a fake.
Using a mock in this case causes pain, as it's not a strong point for
mocks to perform complex actions. If you experience this and think
that mocks suck, you are just not using the right tool for your
problem. Or, you might be trying to solve the wrong problem. :-)
## I got a warning "Uninteresting function call encountered - default action taken.." Should I panic? ##
By all means, NO! It's just an FYI.
What it means is that you have a mock function, you haven't set any
expectations on it (by Google Mock's rule this means that you are not
interested in calls to this function and therefore it can be called
any number of times), and it is called. That's OK - you didn't say
it's not OK to call the function!
What if you actually meant to disallow this function to be called, but
forgot to write `EXPECT_CALL(foo, Bar()).Times(0)`? While
one can argue that it's the user's fault, Google Mock tries to be nice and
prints you a note.
So, when you see the message and believe that there shouldn't be any
uninteresting calls, you should investigate what's going on. To make
your life easier, Google Mock prints the function name and arguments
when an uninteresting call is encountered.
## I want to define a custom action. Should I use Invoke() or implement the action interface? ##
Either way is fine - you want to choose the one that's more convenient
for your circumstance.
Usually, if your action is for a particular function type, defining it
using `Invoke()` should be easier; if your action can be used in
functions of different types (e.g. if you are defining
`Return(value)`), `MakePolymorphicAction()` is
easiest. Sometimes you want precise control on what types of
functions the action can be used in, and implementing
`ActionInterface` is the way to go here. See the implementation of
`Return()` in `include/gmock/gmock-actions.h` for an example.
## I'm using the set-argument-pointee action, and the compiler complains about "conflicting return type specified". What does it mean? ##
You got this error as Google Mock has no idea what value it should return
when the mock method is called. `SetArgPointee()` says what the
side effect is, but doesn't say what the return value should be. You
need `DoAll()` to chain a `SetArgPointee()` with a `Return()`.
See this [recipe](http://code.google.com/p/googlemock/wiki/V1_7_CookBook#Mocking_Side_Effects) for more details and an example.
## My question is not in your FAQ! ##
If you cannot find the answer to your question in this FAQ, there are
some other resources you can use:
1. read other [wiki pages](http://code.google.com/p/googlemock/w/list),
1. search the mailing list [archive](http://groups.google.com/group/googlemock/topics),
1. ask it on [googlemock@googlegroups.com](mailto:googlemock@googlegroups.com) and someone will answer it (to prevent spam, we require you to join the [discussion group](http://groups.google.com/group/googlemock) before you can post.).
Please note that creating an issue in the
[issue tracker](http://code.google.com/p/googlemock/issues/list) is _not_
a good way to get your answer, as it is monitored infrequently by a
very small number of people.
When asking a question, it's helpful to provide as much of the
following information as possible (people cannot help you if there's
not enough information in your question):
* the version (or the revision number if you check out from SVN directly) of Google Mock you use (Google Mock is under active development, so it's possible that your problem has been solved in a later version),
* your operating system,
* the name and version of your compiler,
* the complete command line flags you give to your compiler,
* the complete compiler error messages (if the question is about compilation),
* the _actual_ code (ideally, a minimal but complete program) that has the problem you encounter.
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