---
short-description: Meson's own unit-test system
...

# Unit tests

Meson comes with a fully functional unit test system. To use it simply build an executable and then use it in a test.

```meson
e = executable('prog', 'testprog.c')
test('name of test', e)
```

You can add as many tests as you want. They are run with the command `ninja test`.

Meson captures the output of all tests and writes it in the log file `meson-logs/testlog.txt`.

## Test parameters

Some tests require the use of command line arguments or environment variables. These are simple to define.

```meson
test('command line test', exe, args : ['first', 'second'])
test('envvar test', exe2, env : ['key1=value1', 'key2=value2'])
```

Note how you need to specify multiple values as an array.

### MALLOC_PERTURB_

By default, environment variable
[`MALLOC_PERTURB_`](http://man7.org/linux/man-pages/man3/mallopt.3.html)
is set to a random value between 1..255. This can help find memory
leaks on configurations using glibc, including with non-GCC compilers.
This feature can be disabled as discussed in [test()](./Reference-manual#test).

## Coverage

If you enable coverage measurements by giving Meson the command line flag `-Db_coverage=true`, you can generate coverage reports. Meson will autodetect what coverage generator tools you have installed and will generate the corresponding targets. These targets are `coverage-xml` and `coverage-text` which are both provided by [Gcovr](http://gcovr.com) (version 3.3 or higher) and `coverage-html`, which requires [Lcov](https://ltp.sourceforge.io/coverage/lcov.php) and [GenHTML](https://linux.die.net/man/1/genhtml) or [Gcovr](http://gcovr.com). As a convenience, a high-level `coverage` target is also generated which will produce all 3 coverage report types, if possible.

The output of these commands is written to the log directory `meson-logs` in your build directory.

## Parallelism

To reduce test times, Meson will by default run multiple unit tests in parallel. It is common to have some tests which can not be run in parallel because they require unique hold on some resource such as a file or a D-Bus name. You have to specify these tests with a keyword argument.

```meson
test('unique test', t, is_parallel : false)
```

Meson will then make sure that no other unit test is running at the same time. Non-parallel tests take longer to run so it is recommended that you write your unit tests to be parallel executable whenever possible.

By default Meson uses as many concurrent processes as there are cores on the test machine. You can override this with the environment variable `MESON_TESTTHREADS` like this.

```console
$ MESON_TESTTHREADS=5 ninja test
```

## Priorities

*(added in version 0.52.0)*

Tests can be assigned a priority that determines when a test is *started*. Tests with higher priority are started first, tests with lower priority started later. The default priority is 0, meson makes no guarantee on the ordering of tests with identical priority.

```meson
test('started second', t, priority : 0)
test('started third', t, priority : -50)
test('started first', t, priority : 1000)
```

Note that the test priority only affects the starting order of tests and subsequent tests are affected by how long it takes previous tests to complete. It is thus possible that a higher-priority test is still running when lower-priority tests with a shorter runtime have completed.

## Skipped tests and hard errors

Sometimes a test can only determine at runtime that it can not be run.

For the default `exitcode` testing protocol, the GNU standard approach in this case is to exit the program with error code 77. Meson will detect this and report these tests as skipped rather than failed. This behavior was added in version 0.37.0.

For TAP-based tests, skipped tests should print a single line starting with `1..0 # SKIP`.

In addition, sometimes a test fails set up so that it should fail even if it is marked as an expected failure. The GNU standard approach in this case is to exit the program with error code 99. Again, Meson will detect this and report these tests as `ERROR`, ignoring the setting of `should_fail`. This behavior was added in version 0.50.0.

## Testing tool

The goal of the meson test tool is to provide a simple way to run tests in a variety of different ways. The tool is designed to be run in the build directory.

The simplest thing to do is just to run all tests, which is equivalent to running `ninja test`.

```console
$ meson test
```

### Run subsets of tests

For clarity, consider the meson.build containing:

```meson

test('A', ..., suite: 'foo')
test('B', ..., suite: 'foo')
test('C', ..., suite: 'bar')
test('D', ..., suite: 'baz')

```

Specify test(s) by name like:

```console
$ meson test A D
```

Tests belonging to a suite `suite` can be run as follows

```console
$ meson test --suite (sub)project_name:suite
```

Since version *0.46*, `(sub)project_name` can be omitted if it is the top-level project.

Multiple suites are specified like:

```console
$ meson test --suite foo --suite bar
```

NOTE: If you choose to specify both suite(s) and specific test name(s), the
test name(s) must be contained in the suite(s). This however is redundant--
it would be more useful to specify either specific test names or suite(s).

### Other test options

Sometimes you need to run the tests multiple times, which is done like this:

```console
$ meson test --repeat=10
```

Invoking tests via a helper executable such as Valgrind can be done with the `--wrap` argument

```console
$ meson test --wrap=valgrind testname
```

Arguments to the wrapper binary can be given like this:

```console
$ meson test --wrap='valgrind --tool=helgrind' testname
```

Meson also supports running the tests under GDB. Just doing this:

```console
$ meson test --gdb testname
```

Meson will launch `gdb` all set up to run the test. Just type `run` in the GDB command prompt to start the program.

The second use case is a test that segfaults only rarely. In this case you can invoke the following command:

```console
$ meson test --gdb --repeat=10000 testname
```

This runs the test up to 10 000 times under GDB automatically. If the program crashes, GDB will halt and the user can debug the application. Note that testing timeouts are disabled in this case so `meson test` will not kill `gdb` while the developer is still debugging it. The downside is that if the test binary freezes, the test runner will wait forever.

Sometimes, the GDB binary is not in the PATH variable or the user wants to use a GDB replacement. Therefore, the invoked GDB program can be specified *(added 0.52.0)*:

```console
$ meson test --gdb --gdb-path /path/to/gdb testname
```

```console
$ meson test --print-errorlogs
```

Meson will report the output produced by the failing tests along with other useful information as the environmental variables. This is useful, for example, when you run the tests on Travis-CI, Jenkins and the like.

For further information see the command line help of Meson by running `meson test -h`.

## Legacy notes

If `meson test` does not work for you, you likely have a old version of Meson.
In that case you should call `mesontest` instead. If `mesontest` doesn't work
either you have a very old version prior to 0.37.0 and should upgrade.