Yes, you’re on the right track. What happens await simpleTimer(callback) will wait for the Promise returned by simpleTimer() to resolve so callback() gets called the first time and setTimeout() also gets called. jest.useFakeTimers() replaced setTimeout() with a mock so the mock records that it was called with [ () => { simpleTimer(callback) }, 1000 ]. … Read more
Great solution from @chiedo However, we use ES2015 syntax and I felt it was a little cleaner to write it this way. class LocalStorageMock { constructor() { this.store = {}; } clear() { this.store = {}; } getItem(key) { return this.store[key] || null; } setItem(key, value) { this.store[key] = String(value); } removeItem(key) { delete this.store[key]; … Read more
If you think about the responsibility of the AccessDenied component, it isn’t really to send the user home. That’s the overall behaviour you want, but the component’s role in that is simply to send the user to “/”. At the component unit level, therefore, the test could look something like this: import React, { FC … Read more
Also using Babel, Typescript and Jest. Had the same failure, driving me crazy for hours. Ended up creating a new babel.config.js file specifically for the tests. Had a large .babelrc that wasn’t getting picked up by jest no matter what i did to it. Main app still uses the .babelrc as this overrides babel.config.js files. … Read more
Updated for Jest 27+ For jest 27+, you can also use process.nextTick: await new Promise(process.nextTick); (Thanks to Adrian Godong in the comments) Original Answer Here’s a snippet that waits until pending Promises are resolved: const flushPromises = () => new Promise(setImmediate); Note that setImmediate is a non-standard feature (and is not expected to become standard). … Read more
The following method worked for me. This approach allowed me to test some code that should work both in the browser and in Node.js, as it allowed me to set window to undefined. This was with Jest 24.8 (I believe): let windowSpy; beforeEach(() => { windowSpy = jest.spyOn(window, “window”, “get”); }); afterEach(() => { windowSpy.mockRestore(); … Read more
If an ES6 module directly exports two functions (not within a class, object, etc., just directly exports the functions like in the question) and one directly calls the other, then that call cannot be mocked. In this case, funcB cannot be mocked within funcA the way the code is currently written. A mock replaces the … Read more
From my answer to another question, this can be simpler: The only requirement is to configure your test environment to Babel, and add the ECMAScript 6 transform plugin: Step 1: Add your test environment to .babelrc in the root of your project: { “env”: { “test”: { “plugins”: [“@babel/plugin-transform-modules-commonjs”] } } } Step 2: Install the … Read more
Without using any other libraries: import * as axios from “axios”; // Mock out all top level functions, such as get, put, delete and post: jest.mock(“axios”); // … test(“good response”, () => { axios.get.mockImplementation(() => Promise.resolve({ data: {…} })); // … }); test(“bad response”, () => { axios.get.mockImplementation(() => Promise.reject({ … })); // … }); … 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