This might seem like a lot of work just to get to the same point we had with our first jest module factory approach, but it now opens up a lot of new interesting possibilities. So this line is necessary just to get TypeScript to understand that Jest has modified the module in some way. Instead of mocking every function, jest helps us mimic the entire module using jest.mock. mockFn.mockReset () Does everything that mockFn. But we know that Jest added that while mocking the module. The clearMocks configuration option is available to clear mocks automatically before each tests. If we didn't do this as assignment then TypeScript would forbid us from calling mockImplementation on getUserDetails, because for all TypeScript knows getUserDetails doesn't have a mockImplementation method. But TypeScript doesn't "see" that this has happened, so we have to help it out. The clear, reset, restore distinction isnt the most intuitive. Jest modifies mocked modules at runtime, it does so in a way that leaves the mocked module compatible with its original type but wraps everything to provide mock utility methods such as mockImplementation. Hey all, think this issue is worth looking into again. is that correct? Yes! And it gets at an important little quirk of the way Jest and TypeScript interact. but we also cast it with an as using jest.MockedFunction. Often this is useful when you want to clean up a mocks usage data. It looks like we are assigning the "real" getUserDetails to some fake mockGetUserDetails. Resets all information stored in the and arrays. Import )) Įxpect(screen.getByText( "rupert")).toBeInTheDocument() Let's suppose we have a simple User component that displays the user's name, or "Guest" if no user was found: import * as React from "react" Don't be afraid to mock React components they are just functions!.jest.MockedFunction is the best for type-safe mock functions.
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