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In our first example, the library exports is a single default function. All of those choices affect how the package needs to be mocked in the tests of our application code.īelow, we'll look at some tiny examples to highlight how different exports change our mock strategy. Usage of fetch-mock with Jest is sufficiently different to previous. When publishing a package, the maintainer makes decisions such as choosing default or named exports and whether to export a vanilla function, an object, or a function that returns an object of other functions. fetchMock.reset() or fetchMock.restore() will also restore fetch() to its native. ES6 Exportsīefore we worry about our mock's behavior, it's important to understand how the package we're using is exported.
JEST RESET MOCKS PORTABLE
It's a React app with Jest as the test runner and uses React Testing Library to test the component DOM (this is the default configuration with Create React App).ĭespite being built with React, the mocking examples should be easily portable to any framework. The sample application shows you a random cute image of an animal every 3 seconds. What do we want the behavior of our mock to be?Īll of the following code samples can be found on my Github.When mocking a module or function, there are 2 main things to consider: This is not an exhaustive list, there are multiple ways to satisfy every use case. I created this post to serve as an easily navigable guidebook of strategies for the next time jest.mock('modulename') won't cut it. (Note that resetting a spy will result in a function with no return. Recently, I've been spending more time wrestling with uncooperative mocks than writing the code or the tests combined. This is useful when you want to completely reset a mock back to its initial state.
JEST RESET MOCKS UPDATE
Warning: An update inside a test was not wrapped in act.Cannot set property of # which has only a getter.Cannot spy the default property because it is not a function.If you are trying to use both a mock and the original implementation during the same test there are a few options: Mock one particular function using jest. The module factory of jest.mock() is not allowed to reference any out-of-scope variables There isnt an easy way to restore the original module during a test that uses jest.mock since its primary use is to mock a module for an entire test.Named export of a function that returns an object.Not doing so will result in the internal usage counter not being reset.
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If running multiple tests inside of one file or describe block, eFakeTimers () can be called before each test manually or with a setup function such as beforeEach. Default export of a function that returns an object This mocks out setTimeout and other timer functions with mock functions.