using System;

using Moq;

​

public class Program

{

    public static void Main()

    {

        var mock = new Mock<IFoo>();

        var returnMock = new Mock<IReturn>();

        mock.Setup(f => f.Bar(32)).Returns(returnMock.Object);

        var returnedVal = mock.Object.CallBar();

        Console.WriteLine("Is return value null? " + returnedVal == null);

    }           

}

public interface IFoo

{

    IReturn Bar(int x);

}

​

public interface IReturn

{

}

public static class FooExtension

{

    public static IReturn CallBar(this IFoo foo)

    {

        return foo.Bar(32);

    }

}