Tests fail in Visual Studio 16.2 with could not load file or assembly

Since updating to Visual Studio 2019 16.2 my tests keep failing with this error:

Message: 
    Test method Package.Tests.UnitTest1.TestMethod1 threw exception: 
    FakeItEasy.Core.FakeCreationException: 
      Failed to create fake of type xxxxxx:
        No usable default constructor was found on the type xxxxx.
        An exception of type System.IO.FileNotFoundException was caught during this call. Its message was:
        Could not load file or assembly 'xxxx, Version=x.x.x.x, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.
           at System.Reflection.Emit.TypeBuilder.TermCreateClass(RuntimeModule module, Int32 tk, ObjectHandleOnStack type)
           at System.Reflection.Emit.TypeBuilder.CreateTypeNoLock()
           at System.Reflection.Emit.TypeBuilder.CreateTypeInfo()
           at Castle.DynamicProxy.Generators.Emitters.AbstractTypeEmitter.CreateType(TypeBuilder type) in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at Castle.DynamicProxy.Generators.Emitters.AbstractTypeEmitter.BuildType() in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at Castle.DynamicProxy.Generators.ClassProxyGenerator.GenerateType(String name, Type[] interfaces, INamingScope namingScope) in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at Castle.DynamicProxy.Generators.ClassProxyGenerator.<>c__DisplayClass1_0.<GenerateCode>b__0(String n, INamingScope s) in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at Castle.DynamicProxy.Generators.BaseProxyGenerator.ObtainProxyType(CacheKey cacheKey, Func`3 factory) in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at Castle.DynamicProxy.Generators.ClassProxyGenerator.GenerateCode(Type[] interfaces, ProxyGenerationOptions options) in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at Castle.DynamicProxy.DefaultProxyBuilder.CreateClassProxyType(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options) in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at Castle.DynamicProxy.ProxyGenerator.CreateClassProxy(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options, Object[] constructorArguments, IInterceptor[] interceptors) in C:\projects\fakeiteasy\src\FakeItEasy\Expressions\CallConstraintDescriber.cs:line 0
           at FakeItEasy.Creation.CastleDynamicProxy.CastleDynamicProxyGenerator.GenerateInterfaceProxy(Type typeOfProxy, ReadOnlyCollection`1 additionalInterfacesToImplement, IEnumerable`1 attributes, IFakeCallProcessorProvider fakeCallProcessorProvider) in C:\projects\fakeiteasy\src\FakeItEasy\Creation\CastleDynamicProxy\CastleDynamicProxyGenerator.cs:line 41
    

I have a test project (targeting .net472 and using MsTest) that references a nuget package (let’s call it A) that in turn needs another nuget package (B). I want to create a fake for an interface defined in A. This interface has a property of which the type is an interface defined in B.

In Visual Studio 16.2 this now fails if the version of package B is different than the one listed by package with the error message above.

Now there comes the strange thing:

• This only happens if i run the tests using the Test Explorer. If i run the tests using vstest.console, the tests are successful.
• Using Visual Studio 16.1, everything works
• Visual Studio 2017 works
• Running the tests using resharper works
• In 16.3 preview, it’s broken with the same error.

I’ve been able to reproduce this on different machines using a small project I created with just the things I need.

Reproduce steps on Visual Studio 16.2:

• Create 2 class libraries (X, Y) targeting .net standard and net461
• Define an interface IVeryImportantInterface in X
• Define an interface IMainInterface in Y
  • Add a property of IVeryImportantInterface to the definition (it now has a dependency on X)
• Create nuget packages of both projects and use the same version (2.0.0)
• Create another nugetpackage of the X project and increase the version (3.0.0)
• Create a test project using mstest and .net472
  • Install FakeItEasy
  • Install package Y using packages.config
  • Add this code

      var test = A.Fake<IMainInterface>();
  

• The test should work
• Update the X package to the later version
• The test should now fail

I been trying to wrap my around it why it fails…

[tomeeraerts]

My tests are now working again.

I created a more generic version.

        static UnitTest1()
        {
            AppDomain.CurrentDomain.AssemblyResolve += (sender, args) =>
            {
                 var requestedAssembly = new AssemblyName(args.Name);
                 var loadedAssemblies = AppDomain.CurrentDomain.GetAssemblies();
                 return loadedAssemblies.SingleOrDefault(x =>  x.GetName().Name.Equals(requestedAssembly.Name, StringComparison.OrdinalIgnoreCase));
            };
        }

I’ve put it here in cause anyone has the same problem.

[tomeeraerts]

I’ve create a repo I also included the packages folder, that way you don’t need to create the packages (they were created using dotnet pack).

There are two branches. One using the same versions where the test passes and one using different version where the test fails