public void TestImplementedMethod() { ///I don't understand why you need to use Mocking.Repository class. ///Isn't that an external reference? ///Creates a fake object of Repository ///The fake object is then stored into the Mock<Repository> var mock = new Mock <Repository>(); //Passes the mock object that was created to the Business class //does not pass the Repository to access the methods Business business = new Business(mock.Object); //Test case using the mock object for the implemented method Sum Assert.AreEqual(4, business.Addition(2, 2)); }