Swizec Teller - a geek with a hatswizec.com

    Testing socket.io apps

    Nyan cat testing

    Socket.io is probably one of the coolest things to come out of the JavaScript world in recent years. Finally! Something that lets web developers create real-time apps without the fuss of thinking about websockets and long polling and all the other hacks that need to be used.

    The idea is pretty simple, the server can emit an event and the client will pick it up. The converse also happens. Callbacks through the server-client barrier works as well. Socket.io takes care of deciding which of the real-time hacks should be used to make the magic happen.

    Thing is, the interplay of client and server makes socket.io apps a bit difficult to test.

    A good way I've found is the combination of Mocha, Chai and socket.io-client.

    First, something to test

    Let's take for example a very simple echo server. I used Express to make things easier to play with in the Chrome console. Here's the relevant part of app.js.

    var server = (exports.server = http
    .createServer(app)
    .listen(app.get("port"), function () {
    console.log("Express server listening on port " + app.get("port"));
    }));
    var io = require("socket.io").listen(server);
    io.set("log level", 0);
    // the important parts of echo server
    io.sockets.on("connection", function (socket) {
    socket.on("echo", function (msg, callback) {
    callback = callback || function () {};
    socket.emit("echo", msg);
    callback(null, "Done.");
    });
    });

    After not forgetting to load /socket.io/socket.io.js into the index page, I can now run the server, point my browser to http://localhost:3000 and play around in the console like this:

    > var socket = io.connect("http://localhost:3000")
    undefined
    > socket.on("echo", function (msg) { console.log(msg); })
    SocketNamespace
    > socket.emit("echo", "Hello World")
    SocketNamespace
    Hello World

    Automating the test

    Typing commands into a console, even clicking around a webpage is a rather arduous and boring process. The easiest way I've found to automate this is using Mocha and socket.io-client.

    First thing we're going to need is requiring everything and making sure the socket.io server is running.

    var chai = require('chai'),
    mocha = require('mocha'),
    should = chai.should();
    var io = require('socket.io-client');
    describe("echo", function () {
    var server,
    options ={
    transports: ['websocket'],
    'force new connection': true
    };
    beforeEach(function (done) {
    // start the server
    server = require('../app').server;
    done();
    });

    See, simple :)

    Now comes the interesting part, the actual test making sure our server does in fact echo what we ask it to.

    it("echos message", function (done) {
    var client = io.connect("http://localhost:3000", options);
    client.once("connect", function () {
    client.once("echo", function (message) {
    message.should.equal("Hello World");
    client.disconnect();
    done();
    });
    client.emit("echo", "Hello World");
    });
    });

    The idea behind this test is simple:

    1. Connect client to server
    2. Once there's a connection, listen for echo event from the server
    3. Emit _echo _event to the server
    4. Server responds and triggers our listener
    5. Listener checks correctness of response
    6. Disconnects client

    Disconnecting clients after tests is very important. As I've discovered, not disconnecting can lead to the socket accumulating event listeners, which in turn can fire completely different tests than what you expect. It also leads to tests that pass 70% of the time, but fail in random ways.

    In the end, our efforts are rewarded by a happy nyan cat.

    Nyan cat testing

    PS: you can see all the code on github.

    Maria Ramos from Webhostinghub.com/support/edu has translated this post into Spanish.

    Enhanced by Zemanta

    Did you enjoy this article?

    Published on November 30th, 2012 in Client, JavaScript, Programming, Server, Uncategorized, WebSocket

    Learned something new?
    Want to become an expert?

    Here's how it works 👇

    Leave your email and I'll send you thoughtfully written emails every week about React, JavaScript, and your career. Lessons learned over 20 years in the industry working with companies ranging from tiny startups to Fortune5 behemoths.

    Join Swizec's Newsletter

    And get thoughtful letters 💌 on mindsets, tactics, and technical skills for your career. Real lessons from building production software. No bullshit.

    "Man, love your simple writing! Yours is the only newsletter I open and only blog that I give a fuck to read & scroll till the end. And wow always take away lessons with me. Inspiring! And very relatable. 👌"

    ~ Ashish Kumar

    Join over 14,000 engineers just like you already improving their careers with my letters, workshops, courses, and talks. ✌️

    Have a burning question that you think I can answer? I don't have all of the answers, but I have some! Hit me up on twitter or book a 30min ama for in-depth help.

    Ready to Stop copy pasting D3 examples and create data visualizations of your own?  Learn how to build scalable dataviz components your whole team can understand with React for Data Visualization

    Curious about Serverless and the modern backend? Check out Serverless Handbook, modern backend for the frontend engineer.

    Ready to learn how it all fits together and build a modern webapp from scratch? Learn how to launch a webapp and make your first 💰 on the side with ServerlessReact.Dev

    Want to brush up on your modern JavaScript syntax? Check out my interactive cheatsheet: es6cheatsheet.com

    By the way, just in case no one has told you it yet today: I love and appreciate you for who you are ❤️

    Created bySwizecwith ❤️