The way I did it can be found in this Stack Overflow question. It is important to use resetModules before each test and then dynamically import the module inside the test: describe(‘environmental variables’, () => { const OLD_ENV = process.env; beforeEach(() => { jest.resetModules() // Most important – it clears the cache process.env = { …OLD_ENV … Read more
As of Jest 26 this can be achieved using “modern” fake timers without needing to install any 3rd party modules: https://jestjs.io/blog/2020/05/05/jest-26#new-fake-timers jest .useFakeTimers() .setSystemTime(new Date(‘2020-01-01’)); If you want the fake timers to be active for all tests, you can set timers: ‘modern’ in your configuration: https://jestjs.io/docs/configuration#timers-string EDIT: As of Jest 27 modern fake timers is … Read more
From DOM Testing-library Docs – Appearance and Disappearance Asserting elements are not present The standard getBy methods throw an error when they can’t find an element, so if you want to make an assertion that an element is not present in the DOM, you can use queryBy APIs instead: const submitButton = screen.queryByText(‘submit’) expect(submitButton).toBeNull() // … Read more
You can test your async function like this: it(‘should test async errors’, async () => { await expect(failingAsyncTest()) .rejects .toThrow(‘I should fail’); }); ‘I should fail’ string will match any part of the error thrown.
The docs show you are now able to add: “env”: { “jest/globals”: true } To your .eslintrc which will add all the jest related things to your environment, eliminating the linter errors/warnings. You may need to include plugins: [“jest”] to your esconfig, and add the eslint-plugin-jest plugin if it still isn’t working.
In Jest you have to pass a function into expect(function).toThrow(<blank or type of error>). Example: test(“Test description”, () => { const t = () => { throw new TypeError(); }; expect(t).toThrow(TypeError); }); Or if you also want to check for error message: test(“Test description”, () => { const t = () => { throw new … Read more
Edit: Several years have passed and this isn’t really the right way to do this any more (and probably never was, my bad). Mutating an imported module is nasty and can lead to side effects like tests that pass or fail depending on execution order. I’m leaving this answer in its original form for historical … Read more
The timeout you specify here needs to be shorter than the default timeout. The default timeout is 5000 and the framework by default is jasmine in case of jest. You can specify the timeout inside the test by adding jest.setTimeout(30000); But this would be specific to the test. Or you can set up the configuration … Read more
The Jest docs state it is an alias of test. So they are exactly the same from a functional point of view. They exist both to enable to make a readable English sentence from your test.
Since at least 2019: npm test — bar.spec.js In 2015: In order to run a specific test, you’ll need to use the jest command. npm test will not work. To access jest directly on the command line, install it via npm i -g jest-cli or yarn global add jest-cli. Then simply run your specific test … Read more