Jest (framework)

Jest^[1] is a JavaScript testing framework built on top of Jasmine^[2] and maintained by Meta (formerly Facebook). It was designed and built by Christoph Nakazawa with a focus on simplicity and support for large web applications. It works with projects using Babel, TypeScript, Node.js, React, Angular, Vue.js and Svelte. Jest doesn't require a lot of configuration for first-time users of a testing framework.

Usage and examples

Use the JavaScript package manager npm to install Jest in Node.js:

$ npm install --save-dev jest

In this example, we will write a test case for the following module saved as sum.js:

function sum(a, b) { return a + b; } module.exports = sum;

Our test case will be in a file named sum.test.js for Jest to automatically pick it up as a test case for sum.js.

The contents of the file with the test case will be:

const sum = require('./sum'); test('adds 1 + 2 to equal 3', () => { expect(sum(1, 2)).toBe(3); });

Then, from the command line, we run this command:

$ npm run test

This runs the test and outputs the corresponding result on the command line.

^ "Jest Website".
^ "jest/README.md at 88a94d5d1bc1f387317a3068bf510ab992c5dc64 · facebook/jest". GitHub. Retrieved 2022-05-31.