jest
Advanced tools
Package description
Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It works with projects using: Babel, TypeScript, Node, React, Angular, Vue, and more. It's designed to ensure correctness of any JavaScript codebase. It allows you to write tests with an approachable, familiar, and feature-rich API that gives you results quickly.
Unit Testing
Jest allows you to write unit tests for your JavaScript functions. In this example, a simple test is written to check if the addition of 1 and 2 equals 3.
test('adds 1 + 2 to equal 3', () => {
expect(1 + 2).toBe(3);
});Mocking
Jest provides a powerful mocking library that lets you mock objects, functions, and modules. In this example, an HTTP request is mocked to test the behavior of a function that fetches user data.
jest.mock('../api');
test('should fetch users', () => {
const users = [{name: 'Bob'}];
const resp = {data: users};
axios.get.mockResolvedValue(resp);
return Users.all().then(data => expect(data).toEqual(users));
});Snapshot Testing
Snapshot testing enables you to test your UI or any serializable value to ensure it does not change unexpectedly. This example demonstrates testing an object against a snapshot, with some fields expected to match specific types rather than values.
test('will check the matchers and pass', () => {
const user = {
createdAt: new Date(),
id: Math.floor(Math.random() * 20),
name: 'LeBron James'
};
expect(user).toMatchSnapshot({
createdAt: expect.any(Date),
id: expect.any(Number)
});
});Asynchronous Testing
Jest supports testing of asynchronous code. In this example, an asynchronous function `fetchData` is tested to ensure it resolves with the expected value 'peanut butter'.
test('the data is peanut butter', async () => {
await expect(fetchData()).resolves.toBe('peanut butter');
});Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple. Mocha is often compared to Jest because of its flexible and configurable nature, but it requires more setup and configuration for features like mocking and snapshot testing, which Jest provides out of the box.
Jasmine is a behavior-driven development framework for testing JavaScript code. It does not rely on browsers, DOM, or any JavaScript framework. Similar to Jest, it comes with an easy syntax that makes writing tests simple. However, Jest offers more modern features like snapshot testing and built-in support for test coverage.
AVA is a test runner for Node.js with a concise API, detailed error output, and process isolation that lets you develop with confidence. AVA is designed to handle asynchronous testing more efficiently than Jest but lacks some of Jest's features like snapshot testing and built-in mocking.
Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any JavaScript testing framework. It's often used alongside other testing frameworks like Mocha or Jest to provide more expressive assertions. Unlike Jest, Chai is purely an assertion library and does not provide test runners or mocking utilities.
Changelog
29.5.0
[jest-changed-files] Support Sapling (#13941)[jest-circus, @jest/cli, jest-config] Add feature to randomize order of tests via CLI flag or through the config file(#12922)[jest-cli, jest-config, @jest/core, jest-haste-map, @jest/reporters, jest-runner, jest-runtime, @jest/types] Add workerThreads configuration option to allow using worker threads for parallelization (#13939)[jest-cli] Export yargsOptions (#13970)[jest-config] Add openHandlesTimeout option to configure possible open handles warning. (#13875)[@jest/create-cache-key-function] Allow passing length argument to createCacheKey() function and set its default value to 16 on Windows (#13827)[jest-message-util] Add support for AggregateError (#13946 & #13947)[jest-message-util] Add support for Error causes in test and it (#13935 & #13966)[jest-reporters] Add summaryThreshold option to summary reporter to allow overriding the internal threshold that is used to print the summary of all failed tests when the number of test suites surpasses it (#13895)[jest-runtime] Expose @sinonjs/fake-timers async APIs functions advanceTimersByTimeAsync(msToRun) (tickAsync(msToRun)), advanceTimersToNextTimerAsync(steps) (nextAsync), runAllTimersAsync (runAllAsync), and runOnlyPendingTimersAsync (runToLastAsync) (#13981)[jest-runtime, @jest/transform] Allow V8 coverage provider to collect coverage from files which were not loaded explicitly (#13974)[jest-snapshot] Add support to cts and mts TypeScript files to inline snapshots (#13975)[jest-worker] Add start method to worker farms (#13937)[jest-worker] Support passing a URL as path to worker (#13982)[babel-plugin-jest-hoist] Fix unwanted hoisting of nested jest usages (#13952)[jest-circus] Send test case results for todo tests (#13915)[jest-circus] Update message printed on test timeout (#13830)[jest-circus] Avoid creating the word "testfalse" when takesDoneCallback is false in the message printed on test timeout AND updated timeouts test (#13954)[jest-environment-jsdom] Stop setting document to null on teardown (#13972)[@jest/expect-utils] Update toStrictEqual() to be able to check jest.fn().mock.calls (#13960)[@jest/test-result] Allow TestResultsProcessor type to return a Promise (#13950)[jest-snapshot] Remove dependency on jest-haste-map (#13977)Readme
🃏 Delightful JavaScript Testing
👩🏻💻 Developer Ready: Complete and ready to set-up JavaScript testing solution. Works out of the box for any React project.
🏃🏽 Instant Feedback: Failed tests run first. Fast interactive mode can switch between running all tests or only test files related to changed files.
📸 Snapshot Testing: Jest can capture snapshots of React trees or other serializable values to simplify UI testing.
Read More: https://jestjs.io/
FAQs
Delightful JavaScript Testing.
The npm package jest receives a total of 22,086,712 weekly downloads. As such, jest popularity was classified as popular.
We found that jest demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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