Effective Software Testing

6 Test doubles and mocks

This chapter covers

• Using stubs, fakes, and mocks to simplify testing
• Understanding what to mock, when to mock, and when not to mock
• How to mock the unmockable

Until now, we have been testing classes and methods that were isolated from each other. We passed the inputs to a single method call and asserted its output. Or, when a class was involved, we set up the state of the class, called the method under test, and asserted that the class was in the expected state.

But some classes depend on other classes to do their job. Exercising (or testing) many classes together may be desirable. We often break down complex behavior into multiple classes to improve maintainability, each with a small part of the business logic. We ...