Testing Socket.IO applications

Now let's look at how we can test our chat module. To talk to it from our tests we'll need a Socket.IO client. The Socket.IO project provides another package for this:

> npm install socket.io-client --save-dev

The infrastructure for our tests consists of setting up a server and multiple clients as given here test/realtime/chat.js:

'use strict';
describe('chat', function() {
    const expect = require('chai').expect;
    let server, io, url, createUser, createdClients = [];
    
    beforeEach(done => {
        server = require('http').createServer();
        
        server.listen((err) => {
            if (err) {
                done(err);
            } else {
                const addr = server.address();
                url = 'http://localhost:' + addr.port + '/chat'; 

                io = require('socket.io')(server);
                require('../../src/realtime...