Jest

Jest is a JavaScript testing framework maintained by Facebook, Inc., 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 does not require a lot of configuration for first-time users of a testing framework.

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