2. Spying, stubbing and function assertions
This section of The Jest Handbook is dedicated to improving your understanding of Jest’s rich spying, stubbing and mocking functionality.
You will learn to:
- set, clear and reset mocks, stubs and spies
- assert over spies and mocks
- different approaches to stubbing global objects and testing subclasses
- intercept CommonJS and ESM imports
What are spies, mocks and stubs?
Spies, mocks and stubs fall into the category of test doubles. We’ll use them to check that a function gets called in a test.
We’ll also see how to do setup/teardown and assertions over stubs and spies with Jest.