Let‘s learn how to unit test your JavaScript with Jest, a JavaScript unit testing framework from Facebook. We‘ll install and optimize Jest for this project and see how quick and easy it is to get things going with Jest.

Install:

npm i jest-cli --save-dev

sum.js:

var R = require(‘ramda‘)module.exports = sum;function sum(ary){    return R.sum(ary);}

sum.test.js:

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

Package.json:

Because jest simulate the broswer, so you are able to access ‘window‘ object. But it is really not necessary for Node app.

So, you can config it in package.json:

  "jest": {    "testEnvironment": "node"  },

[Jest] Test JavaScript with Jest