![]() This post goes through how to set, reset and clear mocks, stubs and spies in Jest using techniques such as the beforeEach hook and methods such as jest.clearAllMocks and jest.resetAllMocks. This is why we want to be able to set and modify the implementation and return value of functions in Jest. HTTP requests, database reads and writes are side-effects that are crucial to writing applications. ![]() Systems are inherently side-effectful (things that are not parameters or output values). In unit tests of complex systems, it’s not always possible to keep business logic in pure functions, where the only input are the parameters and the only output is the return value. This is a way to mitigate what little statefulness is in the system. #node Jest set, clear and reset mock/spy/stub implementationīetween test runs we need mocked/spied on imports and functions to be reset so that assertions don’t fail due to stale calls (from a previous test). Join 1000s of developers learning about Enterprise-grade Node.js & JavaScript ![]() Take your JavaScript testing to the next level by learning the ins and outs of Jest, the top JavaScript testing library. Unsplash-logo Bernard Hermant Get The Jest Handbook (100 pages)
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