Mocking internal interfaces

Product.cs

// Product Code

internal interface IFoo
{
    void Bar();
    void Baz();
}

Test.cs

// Test Code
public abstract class MockableFoo : IFoo 
{
    public abstract void Bar();
    public abstract void Baz();
}

...
[Fact]
public void TestBar() {
    var mock = new Mock<MockableFoo>();
    mock.Setup(m => m.Bar()).Returns(...);

    ...
}