Jest can swap out timers with functions that allow you to control the passage of time. You can create a and configure it using setupFilesAfterEnv that can have your mocks inside it and then just import the modules like normal at the top of the test files. Sinon.js and Jest have different ways they approach the concept of mocking. Jest Guides Timer Mocks Version: 28.1 Timer Mocks The native timer functions (i.e., setTimeout (), setInterval (), clearTimeout (), clearInterval ()) are less than ideal for a testing environment since they depend on real time to elapse.
The full set of example code from this article is available on GitHub. Better still, we get that benefit while also making our test code smaller, easier to read and easier to reuse. You have to import the mocked modules after the jest.mock module mocking. Mock Service Worker (MSW) improves unit tests of components that make API calls by defining mocks at the network level instead of mocking our own custom code. Import = require('./someFile') Įxpect(someResult).toBe('Mocked someFunction!') toHaveBeenCalledWith and expect. spyOn() spy/stub/mock assertion reference Jest assert over single or specific argument/parameters with. If I have the following : import React from 'react' To understand which assertions can be used on mocks and stubs see the following posts: Jest.
So this post is intended as a part-guide, part-cheatsheet to refresh your memory when you need to do some mocking. Jest.mock(.) does not seem to work at the ' describe' level for my tests. When writing Jest unit tests, I always struggle to remember the syntax for mocking modules.