George Mauer

using System;
using Xunit;
using Rhino.Mocks;

namespace Sample.Tests {
    // Extension Method
    public interface ISomeInterface {
        void SomeMethod(int param1);

    }
    public static class Extensions {
        public static ISomeInterface SomeMethod(this ISomeInterface someInterface, string someParam) {
            // do work, then call the defined method in the interface
            someInterface.SomeMethod(1);

            return someInterface;
        }

    }

    public class Class1 {
        // tried to do the following but it errors
        [Fact]
        public void SomeMethod_WithSomeInterface_CallsOtherSomeMethod() {
            const string someParam = "something";
            const int someOtherParam = 1;

            var mock = MockRepository.GenerateMock<ISomeInterface>();

            mock.SomeMethod(someParam);

            mock.AssertWasCalled(x => x.SomeMethod(someOtherParam));
        }
    }
}