update csharp README and fix .NET 3.5 build error

csharp/README.md

@@ -31,28 +31,23 @@ which only uses features from C# 3 and earlier.
 Building
 ========
 
-Open the `src/Google.Protobuf.sln` solution in Visual Studio 2015 or
+Open the `src/Google.Protobuf.sln` solution in Visual Studio 2017 or
 later.
 
 Although *users* of this project are only expected to have Visual
 Studio 2012 or later, *developers* of the library are required to
-have Visual Studio 2015 or later, as the library uses C# 6 features
-in its implementation. These features have no impact when using the
-compiled code - they're only relevant when building the
-`Google.Protobuf` assembly.
+have Visual Studio 2017 or later, as the library uses C# 6 features
+in its implementation, as well as the new Visual Studio 2017 csproj 
+format. These features have no impact when using the compiled code - 
+they're only relevant when building the `Google.Protobuf` assembly.
 
 Testing
 =======
 
-The unit tests use [NUnit 3](https://github.com/nunit/nunit). Vanilla NUnit doesn't 
-support .NET Core, so to run the tests you'll need to use 
-[dotnet-test-nunit](https://github.com/nunit/dotnet-test-nunit). 
-`dotnet-test-nunit` can also run tests for .NET 4.5+, so to run the tests 
-for both .NET Core and .NET 4.5, you can simply open the 
-`Package Manager Console` in Visual Studio and execute:
-```
-dotnet test Google.Protobuf.Test
-```
+The unit tests use [NUnit 3](https://github.com/nunit/nunit). NUnit doesn't yet
+support `dotnet test`, so for now the test project is a console application 
+using NUnitLite. Simply run `Google.Protobuf.Test.exe` to run the unit tests 
+directly, or else use `dotnet run`.
 
 .NET 3.5
 ========
@@ -62,35 +57,15 @@ to make enabling .NET 3.5 support relatively painless in case you require it.
 There's no guarantee that this will continue in the future, so rely on .NET 
 3.5 support at your peril.
 
-To enable .NET 3.5 support:
-
-1. Modify [src/Google.Protobuf/project.json](src/Google.Protobuf/project.json) to add `"net35": {}` to `"frameworks"`.
-2. Modify [src/Google.Protobuf.Test/project.json](src/Google.Protobuf/project.json):
-  1. Add `"net35": {}` to `"frameworks"`.
-  2. `dotnet-test-nunit` doesn't support .NET 3.5, so remove it from 
-  the project-wide `"dependencies"` and add it to the framework-specific 
-  dependencies under `"net451"` and `"netcoreapp1.0"`.
-
-Note that `dotnet-test-nunit` doesn't support .NET 3.5. You can instead run the 
-tests with [NUnit 3 console](https://github.com/nunit/nunit-console) 
-by running something like: 
-```
-nunit3-console.exe "Google.Protobuf.Test\bin\Debug\net35\win7-x64\Google.Protobuf.Test.dll" --inprocess
-```
-
-The exact path may differ depending on your environment (e.g., the `win7-x64` 
-directory may be called something else). The `--inprocess` flag seems to be a 
-necessary workaround for a bug in NUnit; otherwise, you'll receive 
-an error "Exception has been thrown by the target of an invocation" 
-([possibly related issue](https://github.com/nunit/nunit/issues/1480)).
-
-If you still want to run the .NET 4.5 and .NET Core tests, you can do so by 
-specifying the framework when using `dotnet-test-nunit`, i.e. from 
-`Package Manager Console` in Visual Studio:
-```
-dotnet test Google.Protobuf.Test --framework netcoreapp1.0
-dotnet test Google.Protobuf.Test --framework net451
-```
+To enable .NET 3.5 support, you must edit the `TargetFrameworks` elements of 
+[src/Google.Protobuf/Google.Protobuf.csproj](src/Google.Protobuf/Google.Protobuf.csproj) 
+(and [src/Google.Protobuf.Test/Google.Protobuf.Test.csproj](src/Google.Protobuf.Test/Google.Protobuf.Test.csproj) 
+if you want to run the unit tests): 
+
+Open the .csproj file in a text editor and simply add `net35` to the list of 
+target frameworks, noting that the `TargetFrameworks` element appears twice in 
+the file (once in the first `PropertyGroup` element, and again in the second 
+`PropertyGroup` element, i.e., the one with the conditional).
 
 History of C# protobufs
 =======================

csharp/src/Google.Protobuf.Test/Program.cs

@@ -38,7 +38,11 @@ namespace Google.Protobuf.Test
     {
         public static int Main(string[] args)
         {
+            #if NET35
+                return new AutoRun(typeof(Program).Assembly).Execute(args);
+            #else
                 return new AutoRun(typeof(Program).GetTypeInfo().Assembly).Execute(args);
+            #endif
         }
     }
 }