iOS Unit Testing by Example

Replace the Difficult Dependency with a Mock Object

This chapter focuses on refactoring ChangePasswordViewController, so we want to bring it under test. But the class has an embedded dependency on PasswordChanger. Even though PasswordChanger is a simulation, we need to break this dependency. We shouldn’t have unit tests call an actual web service, not even one set up for testing. It’s unreliable, too slow, and would pollute the service.

Instead, let’s apply ​Extract a Protocol to Support Test Doubles​. In PasswordChanger.swift, define an empty protocol named PasswordChanging:

Refactoring/Refactoring/PasswordChanger.swift

protocol PasswordChanging {}

Then in ChangePasswordViewController, change the passwordChanger property to have an ...