c# - Mocking generic method call for any given type parameter

Question

I have an interface

public interface IDataProvider
{
    T GetDataDocument<T>(Guid document) where T:class, new()
}

I'd like to mock it in a way, that it would just return a new instance of a given type, regardless of the exact type, something like:

myMock.Setup(m => m.GetDataDocument<It.IsAny<Type>()>(It.IsAny<Guid>()))
.Returns(() => new T());

(which doesn't work of course, because I cannot just give any type parameter to moq, and I can't know which type must be returned.

Any ideas on this one?

Answer 1

Instead of using a mock, maybe your case would be better to use a Stub.

public class StubDataProvider : IDataProvider
{
    public T GetDataDocument<T>(Guid document) where T : class, new()
    {
        return new T();
    }
}

If you truly need a mock (so you can verify that GetDataDocument was called). Instead of trying to wrestle with a Mocking framework it sometimes is easier to just create a Mock class out right.

public class MockDataProvider : IDataProvider
{
    private readonly Action _action;

    public MockDataProvider(Action action)
    {
        _action = action;
    }

    public T GetDataDocument<T>(Guid document) where T : class, new()
    {
        _action();
        return new T();
    }
}

And than in your test:

bool wasCalled = false;
IDataProvider dataProvider = new MockDataProvider(() => { wasCalled = true; });
var aTable = dataProvider.GetDataDocument<ATable>(new Guid());
Debug.Assert(wasCalled);