I am trying to test the logic from some existing classes. It is not possible to re-factor the classes at present as they are very complex and in production.

What I want to do is create a mock object and test a method that internally calls another method that is very hard to mock.

So I want to just set a behaviour for the secondary method call.

But when I setup the behaviour for the method, the code of the method is invoked and fails.

Am I missing something or is this just not possible to test without re-factoring the class?

I have tried all the different mock types (Strick,Stub,Dynamic,Partial ect.) but they all end up calling the method when I try to set up the behaviour.

using System;
using MbUnit.Framework;
using Rhino.Mocks;

namespace MMBusinessObjects.Tests
{
    [TestFixture]
    public class PartialMockExampleFixture
    {
        [Test]
        public void Simple_Partial_Mock_Test()
        {
            const string param = "anything";

            //setup mocks
            MockRepository mocks = new MockRepository();


            var mockTestClass = mocks.StrictMock<TestClass>();

            //record beahviour *** actualy call into the real method stub ***
            Expect.Call(mockTestClass.MethodToMock(param)).Return(true);

            //never get to here
            mocks.ReplayAll();

            //this is what i want to test
            Assert.IsTrue(mockTestClass.MethodIWantToTest(param));


        }

        public class TestClass
        {
            public bool MethodToMock(string param)
            {
                //some logic that is very hard to mock
                throw new NotImplementedException();
            }

            public bool MethodIWantToTest(string param)
            {
                //this method calls the 
                if( MethodToMock(param) )
                {
                    //some logic i want to test
                }

                return true;
            }
        }
    }
}