Unit testing C++ CLR

Question

What is the best approach to write Unit Tests for C++/CLR?

We have a solution that includes C++ native, C++/CLR and C#.Net code.

When I try to add a C++/CLR reference to a C#.net Unit Test project, it compiles, but when I run the tests it says "Could not load file or assembly".
Copy-Local is true and it is in the same directory as the C# assambly under test.

Answer 1

Hi @Günther Humer ,

Welcome to Microsoft Q&A forum.

Have you also tried to use Native Unit Test Project? And in this Native Unit Test project, see if property => Configuration Properties => Advanced => C++/CLI Properties options help.

Best Regards,
Tianyu

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Answer 2

TLDR

Custom AssemblyResolve in a C++/CLR-project, which has to be set up (SetUpAssemblyResolve()) before running the tests.
It simply tries to load the Assembly from "./"

using namespace System;  
using namespace ::System::Reflection;  
using namespace System::IO;  
  
Assembly^ OnAssemblyResolve(System::Object^ obj, System::ResolveEventArgs^ args)  
{  
auto requestedName = gcnew AssemblyName(args->Name);  
  
  auto assemblyPath = Path::GetFullPath(Path::Combine("./", requestedName->Name + ".dll"));  
  if (!File::Exists(assemblyPath)) {  
    assemblyPath = Path::GetFullPath(Path::Combine("./", requestedName->Name + ".exe"));  
    if (!File::Exists(assemblyPath))  
      return nullptr;  
  }  
    
  auto assembly = Assembly::LoadFrom(assemblyPath);  
  return assembly;  
}  
  
void SetUpAssemblyResolve()  
{  
AppDomain::CurrentDomain->AssemblyResolve += gcnew System::ResolveEventHandler(&OnAssemblyResolve);  
}  

I created a test-project where you can see the problems. And I also found a solution.

The TestProject can be found here:
https://github.com/relascope/TestingCppClrCs/

This Commit still has problems:
https://github.com/relascope/TestingCppClrCs/commit/c943d806db2deba5470cbb49994371cbbf92331e

Native C++ Tests calling Dll Calling C++/CLR calling C#-assembly fails to load the assembly.
Setting the test project to compile with /clr does not help, the tests disappear. Anyway, this does not matter, since calling into C++/CLR-Dll is possible the same way like calling native code, and it doesn't really matter, if the test-code itself is native C++ or C++/CLR.

/Diag:testdiagnostics.log
shows, that the vstest.console.exe tries to load the assemblies only from some Visual Studio folders.
"./" is not searched.

Since we cannot mock away all C# calls (Solution is too big and has grown over the years and some Interfaces are in C#), it is essential to use it.

One way would be to use google-test (which has no problem loading the C# assemblies), but here we are facing difficulties with Typemocks Isolator++.

The Solution for now is to use AppDomain::CurrentDomain->AssemblyResolve to register a custom AssemblyResolver, which just tries to load from "./".
For the testing spike, this solution is sufficient (can be seen in the latest commit of the TestingCppClrCs Project).

The next step will be the integration into our real project.