Fakes and Mocks

A test double is any type that takes the place of a real dependency during a test. The term covers three kinds of type, and engineers often use their names as if they meant the same thing. A stub returns fixed answers. A fake is a small working implementation, such as a store backed by a map instead of a database. A mock records the calls it receives, so that a test can check which calls were made.

All three satisfy the same interface, so the code under test uses them all in the same way