Test SUSI Web App with Facebook Jest

Jest is used by Facebook to test all Javascript codes specially React code snippets. If you need to setup jest on your react application you can follow up these simple steps. But if your React application is made with “create-react-app”, you do not need to setup jest manually. Because it comes with Jest. You can run test using “react-scripts” node module.

Since SUSI chat is made with “create-react-app” we do not need to install and run Jest directly. We executed our test cases using “npm test” it executes “react-scripts test” command. It executes all “.js” files under “__tests__” folders. And all other files with “.spec.js” and “.test.js” suffixes.

React apps that are made from “create-react-app” come with sample test case (smoke test) and that checks whether whole application is built correctly or not. If it passes the smoke test then it starts to run further test cases.

import React from 'react';
import ReactDOM from 'react-dom';
import ChatApp from '../../components/ChatApp.react';
it('renders without crashing', () => {
 const div = document.createElement('div');
 ReactDOM.render( < ChatApp / > , div);

This checks all components which are inside of the “<ChatApp />” component and it check whether all these components integrate correctly or not.

If we need to check only one component in isolated environment. We can use shallow rendering API. we have used shallow rendering API to check each and every component in isolated environment.

We have to install enzyme and test renderer before use it.

npm install --save-dev enzyme react-test-renderer

import React from 'react';
import MessageSection from '../../components/MessageSection.react';
import { shallow } from 'enzyme';
it('render MessageListItem without crashing',()=>{
  shallow(<MessageSection />);

This test case tests only the “MessageListItem”, not its child components.

After executing “npm test” you will get the passed and failed number of test cases.

If you need to see the coverage you can see it without installing additional dependencies.

You just need to run this.

npm test -- --coverage

It will show the output like this.

This view shows how many lines, functions, statements, branches your program has and this shows how much of those covered from the test cases you have.

If we are going to write new test cases for susi chat, we have to make separate file in “__tests__” folder and name it with corresponding file name that we are going to test.

it('your test case description',()=>{
 //test what you need 

Normally test cases looks like this.in test cases you can use “test” instead of “it” .after test case description, there is a fat arrow function. In side this fat arrow function you can add what you need to test

In below example I have compared returned value of the function with static value.

function funcName(){
 return 1;

it('your test case description',()=>{

You have to add your function/variable that need to be tested into “expect()” and value you expect from that function or variable into “toBe()”.  Instead of “toBe()” you can use different functions according to your need.

If you have a long list of test cases you can group them ( using describe()).

describe('my beverage', () => {
  test('is delicious', () => {

  test('is not sour', () => {

This post covers only few things of testing . You can learn more about jest testing from official documentation here.