The Purpose of Mocking

Question

What is the purpose of mocking?

I have been following some ASP.NET MVC tutorials that use NUnit for testing and Moq for mocking. I am a little unclear about the mock

Answer 1

One other answer :

• Stub = fake objects to be able to run your test without the entire real context

• Mock = fake object to record the interaction of your component and verify theses interactions

You can have several stubs in one test but only one mock because if you have more than one mock you certainly test more than one feature (and it defeat the purpose of the test-one-thing principle).

To go beyond the basics, Mocks are more behavioral verification than the traditionnal state verification of the test where you check the state of your component after acting on it (Arrange,Act, Assert with Mocks it is more Arrange, Act, Verify) :

State verification Assert.AreEqual(valueExpected,mycomponent.Property); Behavioral verification : myMock.WasCalled(MyMethod);

Answer 2

"Mock" is a heavily overloaded term in testing & TDD circles. See Martin Fowler's article Mocks Aren't Stubs. A "proper" mock knows what values it's supposed to receive and lets you know when it doesn't get what was intended; this allows you to do interaction testing instead of state testing - you verify that the class under test is passing the correct messages to its collaborators, in the correct sequence. Interaction testing is quite different from conventional state testing and can be hard to get your head around. Keeping in mind that interaction testing is the point of mocks may make them easier to understand.