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The package jest-fetch-mock gives us more control and avoids us having to handle the double promise response that fetch has. After installing the package, if you are using create-react-app, there is already a file named src/setupTests.js where you can put global Jest code.You can create a mock function with jest.fn(). If no implementation is given, the mock function will Beware that mockFn.mockRestore only works when the mock was created with jest.spyOn. mockFn.mockImplementation(fn). Accepts a function that should be used as the implementation of...

Nov 12, 2018 · You have a module that exports multiple functions. One of these functions depends on another function of the same module. This would seem to be a classic situation for using Jest functionalities… Mock functions are also known as "spies", because they let you spy on the behavior of a function that is called indirectly by some other code, rather than only testing the output. You can create a mock function with `jest.fn()`. If no implementation is given, the mock function will return `undefined` when invoked.