Dealing with dependencies in tests

This document discusses different types of test doubles (fakes, stubs, mocks, spies, and dummies) that can be used to deal with dependencies in tests. It explains what each type is and provides examples of when each might be used. It also discusses how to design code for better test isolation by reducing coupling and avoiding tightly binding components together, though this can sometimes make the code harder to test. Cross-cutting concerns like authentication are discussed as things that may be difficult to fully isolate or mock at a component level.