7.2. Testing with mocks

The point of unit testing is to test as many aspects of your code as possible in isolation from the other parts; it’s easier to tightly specify the behavior of your code and makes the tests run faster. In practice, life is never quite so neat. Your objects need to interact with other objects, and you need to test that interaction. Several different approaches can minimize the number of live objects your tests need to use; the most useful of these approaches is creating mock objects.

7.2.1. Mock objects

Working with mock objects is one place where you’ll see the advantage of using a dynamically typed language. In a statically typed language, the compiler won’t let you run any code unless the types match those declared in the production code. The objects you use in tests must be real objects, or objects that inherit from the expected type.