Interface method does not have an implementation exception

When I upgraded a project today from 3.X to latests version 4.1.1 i got a odd error.

I have an interface like below and got the following error when calling A.Fake<Test>();

public interface Test
{
	void Test1<T>(IEnumerable<T> enumerable);
	void Test1<T>(IList<T> enumerable);
}

*ERROR

FakeCreationException: 
  Failed to create fake of type UserQuery+Test.

  Below is a list of reasons for failure per attempted constructor:
    No constructor arguments failed:
      No usable default constructor was found on the type UserQuery+Test.
      An exception of type System.TypeLoadException was caught during this call. Its message was:
      Method 'Test1' in type 'Castle.Proxies.ObjectProxy_9' from assembly 'DynamicProxyGenAssembly2, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' does not have an implementation.
         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\AsyncReturnValueConfigurationExtensions.cs:line 0
         at Castle.DynamicProxy.Generators.Emitters.AbstractTypeEmitter.BuildType() in C:\projects\fakeiteasy\src\FakeItEasy\AsyncReturnValueConfigurationExtensions.cs:line 0
         at Castle.DynamicProxy.Generators.ClassProxyGenerator.GenerateType(String name, Type[] interfaces, INamingScope namingScope) in C:\projects\fakeiteasy\src\FakeItEasy\AsyncReturnValueConfigurationExtensions.cs:line 0
         at Castle.DynamicProxy.Generators.ClassProxyGenerator.<>c__DisplayClass1_0.<GenerateCode>b__0(String n, INamingScope s) in C:\projects\fakeiteasy\src\FakeItEasy\AsyncReturnValueConfigurationExtensions.cs:line 0
         at Castle.DynamicProxy.Generators.BaseProxyGenerator.ObtainProxyType(CacheKey cacheKey, Func`3 factory) in C:\projects\fakeiteasy\src\FakeItEasy\AsyncReturnValueConfigurationExtensions.cs:line 0
         at Castle.DynamicProxy.Generators.ClassProxyGenerator.GenerateCode(Type[] interfaces, ProxyGenerationOptions options) in C:\projects\fakeiteasy\src\FakeItEasy\AsyncReturnValueConfigurationExtensions.cs:line 0
         at Castle.DynamicProxy.DefaultProxyBuilder.CreateClassProxyType(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options) in C:\projects\fakeiteasy\src\FakeItEasy\AsyncReturnValueConfigurationExtensions.cs:line 0
         at Castle.DynamicProxy.ProxyGenerator.CreateClassProxy(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options, Object[] constructorArguments, IInterceptor[] interceptors) in C:\projects\fakeiteasy\src\FakeItEasy\AsyncReturnValueConfigurationExtensions.cs:line 0
         at FakeItEasy.Creation.CastleDynamicProxy.CastleDynamicProxyGenerator.GenerateClassProxy(Type typeOfProxy, ProxyGenerationOptions options, IEnumerable`1 argumentsForConstructor, IInterceptor interceptor, IEnumerable`1 allInterfacesToImplement) in C:\projects\fakeiteasy\src\FakeItEasy\Creation\CastleDynamicProxy\CastleDynamicProxyGenerator.cs:line 174
         at FakeItEasy.Creation.CastleDynamicProxy.CastleDynamicProxyGenerator.DoGenerateProxy(Type typeOfProxy, ProxyGenerationOptions options, IEnumerable`1 additionalInterfacesToImplement, IEnumerable`1 argumentsForConstructor, IInterceptor interceptor) in C:\projects\fakeiteasy\src\FakeItEasy\Creation\CastleDynamicProxy\CastleDynamicProxyGenerator.cs:line 159
         at FakeItEasy.Creation.CastleDynamicProxy.CastleDynamicProxyGenerator.CreateProxyGeneratorResult(Type typeOfProxy, ProxyGenerationOptions options, IEnumerable`1 additionalInterfacesToImplement, IEnumerable`1 argumentsForConstructor, IFakeCallProcessorProvider fakeCallProcessorProvider) in C:\projects\fakeiteasy\src\FakeItEasy\Creation\CastleDynamicProxy\CastleDynamicProxyGenerator.cs:line 105

This works fine prior to 4.1.0 (both 3.X and 4.0.0).

I suspect it’s the upgrade of Castle.Core 4.1 to 4.2, but I’m unsure, because if I add a reference to Castle.Core 4.2.1 in my project it still work with FakeItEasy 4.0.0 and earlier.

[blairconrad]

Oh, it’s nearly always faster for us to do it, but we very much enjoy community contributions (and assume that the community members enjoy making them - if I’m wrong here, please correct me).

If nothing else, I’m in mid-East Canada time, so you can always report back tonight with your progress and/or feelings, and I’ll be awake. 😉

I will warn you, though, that I’d enjoy a new spec for the use case. I would add a new Scenario to CreationSpecsBase. If you’ve not used xBehave.net before, fret not, since it’s a joy to use and the examples in that file are good to copy. In particular, CollectionOfFakeWithOptionBuilder is a good starting point (except that you’d only make one fake, of course).

The only tricky part about the test would be that since CreationSpecsBase is an abstract base class designed to test both generic and non-generic test creation methods. I’d create your fake using this.CreateFake<>() instead of the standard A.Fake<>().

Again, thanks for raising the issue and for agreeing to help us fix it!

[skarum]

I can do that 😃 I’ll look at it tonight (Europe time) and make a PR. If it’'s faster for you to make it yourself, then just go ahead.