How are Mocks meant to be used?

Question

When I originally was introduced to Mocks I felt the primary purpose was to mock up objects that come from external sources of data. This way I did not have to maintain an

Answer 1

I recommend you take a look at Martin Fowler's article Mocks Aren't Stubs for a more authoritative treatment of Mocks than I can give you.

The purpose of mocks is to unit test your code in isolation of dependencies so you can truly test a piece of code at the "unit" level. The code under test is the real deal, and every other piece of code it relies on (via parameters or dependency injection, etc) is a "Mock" (an empty implementation that always returns expected values when one of its methods is called.)

Mocks may seem tedious at first, but they make Unit Testing far easier and more robust once you get the hang of using them. Most languages have Mock libraries which make mocking relatively trivial. If you are using Java, I'll recommend my personal favorite: EasyMock.

Let me finish with this thought: you need integration tests too, but having a good volume of unit tests helps you find out which component contains a bug, when one exists.