FakeItEasy - Having an interface fake inherit from abstract while both share same interface inheritance

Question

I have an interface

public interface IInterface { void DoSomething(); }

Another interface

public interface IOtherInterface : IInterface { }

An abstract class

public abstract class AbstractClass : IInterface
{
    public void DoSomething()
    {
        Console.WriteLine("Got here");
    }
}

I'm writing a unit test and fake IOtherInterface. The abstract class already contains helpful methods I'd want to leverage for my unit test. How would I make my A.Fake<IOtherInterface>(); inherit from AbstractClass?

This is what I've tried so far but it doesn't work - AbstractClass.DoSomething does not get hit.

        IOtherInterface fake = A.Fake<IOtherInterface>(builder => builder.Implements(typeof (AbstractClass)));

        fake.DoSomething();

Of course if I make a proxy like:

        var abstractFake = A.Fake<AbstractClass>();
        A.CallTo(() => fake.DoSomething()).Invokes(abstractFake.DoSomething);

        fake.DoSomething();

... things work as I wanted. Is there a built in mechanism to achieve this so that I don't need that proxy abstractFake object?

UPDATE

I need IOtherInterface because I have a client class that needs that IOtherInterface as dependency:

class Consumer
{
    public Consumer(IOtherInterface otherInterface)
    {
        otherInterface.DoSomething();
    }
}

Answer 1

var fake = (IOtherInterface) A.Fake<AbstractClass>(builder =>
                               builder.Implements(typeof(IOtherInterface)));
A.CallTo(() => fake.DoSomething()).CallsBaseMethod();
fake.DoSomething();

Implements is intended to work only with interfaces, so the proper way to use it is to fake an interface or class and use Implements to add additional interface. I think it should've complained at you, so I raised complain when IFakeOptionsBuilder.Implements is passed a non-interface, which was fixed in FakeItEasy 2.0.0.

The CallsBaseMethod will ensure that the Abstract class's method is executed.

I would've recommended builder.CallsBaseMethods(), but this fails to redirect the call. I think it's because it's redirecting AbstractClass.DoSomething, but when we cast the fake to IOtherInterface and call DoSomething, it's not matching. I've raised investigate interaction between Implements and CallsBaseMethods.