Welcome!

Eclipse Authors: Roger Strukhoff, Carmen Gonzalez, Lori MacVittie, Kevin Jackson, Mark R. Hinkle

Blog Feed Post

Testing your Frontend JavaScript code using Mocha, Chai and Sinon

Testing your frontend JavaScript code using mocha, chai, and sinon by Nicolas Perriault

This is a republished blog post by Nicolas Perriault. When I first read it I immediately thought it would fit perfectly on our Codeship blog. You may know Nicolas for his awesome CasperJS (an open source navigation scripting & testing utility written in Javascript for PhantomJS) or from various of his talks. We highly recommend following Nicolas on twitter and checking out his website.


As rich Web application complexity grows, if you want to keep your sanity, you need to unit test your frontend JavaScript code.

For the 4 past months, I’ve been working for Mozilla on some big project where such testing strategy was involved. While I wish we could use CasperJS in this perspective, Firefox wasn’t supported at the time and we needed to ensure proper compatibility with its JavaScript engine. So we went with using Mocha, Chai and Sinon and they have proven to be a great workflow for us so far.

The mocha testing framework and the chai expectation library

Mocha is a test framework while Chai is an expectation one. Let’s say Mocha sets up and describes test suites and Chai provides convenient helpers to perform all kinds of assertions against your JavaScript code.

So let’s say we have a Cow object we want to unit test:

// cow.js
(function(exports) {
  "use strict";

  function Cow(name) {
    this.name = name || "Anon cow";
  }
  exports.Cow = Cow;

  Cow.prototype = {
    greets: function(target) {
      if (!target)
        throw new Error("missing target");
      return this.name + " greets " + target;
    }
  };
})(this);

Nothing fancy, but we want to unit test this one.

Both Mocha and Chai can be used in a Node environment as well as within the browser; in the latter case, you’ll have to setup a test HTML page and use special builds of those libraries:

My advice is to store these files in a vendor subfolder. Let’s create a HTML file to test our lib:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>Cow tests</title>
  <link rel="stylesheet" media="all" href="vendor/mocha.css">
</head>
<body>
  <div id="mocha"><p><a href=".">Index</a></p></div>
  <div id="messages"></div>
  <div id="fixtures"></div>
  <script src="vendor/mocha.js"></script>
  <script src="vendor/chai.js"></script>
  <script src="cow.js"></script>
  <script>mocha.setup('bdd')</script>
  <script src="cow_test.js"></script>
  <script>mocha.run();</script>
</body>
</html>

Please note we’ll be using Chai’s BDD Expect API, hence the mocha.setup('bdd') call here.

Now let’s write a simple test suite for our Cow object constructor in cow_test.js:

var expect = chai.expect;

describe("Cow", function() {
  describe("constructor", function() {
    it("should have a default name", function() {
      var cow = new Cow();
      expect(cow.name).to.equal("Anon cow");
    });

    it("should set cow's name if provided", function() {
      var cow = new Cow("Kate");
      expect(cow.name).to.equal("Kate");
    });
  });

  describe("#greets", function() {
    it("should throw if no target is passed in", function() {
      expect(function() {
        (new Cow()).greets();
      }).to.throw(Error);
    });

    it("should greet passed target", function() {
      var greetings = (new Cow("Kate")).greets("Baby");
      expect(greetings).to.equal("Kate greets Baby");
    });
  });
});

Tests should be passing, so if you open the HTML document in your browser, you should get something like:

Testing your frontend JavaScript code using mocha, chai, and sinon

If any of these expectations fails, you’ll be notified in the test results, eg. if we change the implementation of greets as below:

Cow.prototype = {
    greets: function(target) {
      if (!target)
        throw new Error("missing target");
      return this.name + " greets " + target + "!";
    }
  };<img src="http://blog.codeship.io/wp-content/uploads/2014/01/2_n1k0_cow-tests-ko.jpg" alt="Testing your frontend JavaScript code using mocha, chai, and sinon" width="885" height="382" class="alignnone size-full wp-image-670" />

You’ll get this instead:

Testing your frontend JavaScript code using mocha, chai, and sinon

How about testing asynchronous stuff?

Now imagine we implement a Cow#lateGreets method so the greetings come with a delay of one second:

Cow.prototype = {
    greets: function(target) {
      if (!target)
        throw new Error("missing target");
      return this.name + " greets " + target + "!";
    },

    lateGreets: function(target, cb) {
      setTimeout(function(self) {
        try {
          cb(null, self.greets(target));
        } catch (err) {
          cb(err);
        }
      }, 1000, this);
    }
  };

We need to test this one as well, and Mocha helps us with its optional done callback for tests:

describe("#lateGreets", function() {
    it("should pass an error if no target is passed", function(done) {
      (new Cow()).lateGreets(null, function(err, greetings) {
        expect(err).to.be.an.instanceof(Error);
        done();
      });
    });

    it("should greet passed target after one second", function(done) {
      (new Cow("Kate")).lateGreets("Baby", function(err, greetings) {<img src="http://blog.codeship.io/wp-content/uploads/2014/01/3_n1k0_cow-async-tests-ok.jpg" alt="Testing your frontend JavaScript code using mocha, chai, and sinon – timed out" width="885" height="402" class="alignnone size-full wp-image-671" />
        expect(greetings).to.equal("Kate greets Baby");
        done();
      });
    });
  });

Conveniently, Mocha will highlight any suspiciously long operation with red pills in case it wasn’t really expected:

Testing your frontend JavaScript code using mocha, chai, and sinon – timed out

Using Sinon for faking the environment

When you do unit testing, you don’t want to depend on stuff external to the unit of code under test. And while avoiding your functions to have side effects is usually a good practice, in Web development it’s not always easy task (think DOM, Ajax, native browser APIs, etc.)

Sinon is a great JavaScript library for stubbing and mocking such external dependencies and to keep control on side effects against them.

As an example, let’s imagine that our Cow#greets method wouldn’t return a string but rather directly log them onto the browser console:

// cow.js
(function(exports) {
  "use strict";

  function Cow(name) {
    this.name = name || "Anon cow";
  }
  exports.Cow = Cow;

  Cow.prototype = {
    greets: function(target) {
      if (!target)
        return console.error("missing target");
      console.log(this.name + " greets " + target);
    }
  };
})(this);

How to unit test this? Well, Sinon to the rescue! First, let’s add the Sinon script to our HTML test file:

<!-- ... -->
<script src="vendor/mocha.js"></script>
<script src="vendor/chai.js"></script>
<script src="vendor/sinon-1.7.1.js"></script>

We’ll stub the console object’s log and error methods so we can check they’re called and what’s passed to them:

var expect = chai.expect;

describe("Cow", function() {
  var sandbox;

  beforeEach(function() {
    // create a sandbox
    sandbox = sinon.sandbox.create();

    // stub some console methods
    sandbox.stub(window.console, "log");
    sandbox.stub(window.console, "error");
  });

  afterEach(function() {
    // restore the environment as it was before
    sandbox.restore();
  });

  // ...

  describe("#greets", function() {
    it("should log an error if no target is passed in", function() {
      (new Cow()).greets();

      sinon.assert.notCalled(console.log);
      sinon.assert.calledOnce(console.error);
      sinon.assert.calledWithExactly(console.error, "missing target")
    });

    it("should log greetings", function() {
      var greetings = (new Cow("Kate")).greets("Baby");

      sinon.assert.notCalled(console.error);
      sinon.assert.calledOnce(console.log);
      sinon.assert.calledWithExactly(console.log, "Kate greets Baby")
    });
  });
});

Several things to be noticed here:

  • beforeEach and afterEach are part of the Mocha API and allow to define setup and tear down operations for each test;
  • Sinon provides sandboxing, basically allowing to define and attach a set of stubs to a sandbox object you’ll be able to restore at some point;
  • When stubbed, real functions are not called at all, so here obviously nothing will be printed onto the browser console;
  • Sinon ships with its own assertion library, hence the sinon.assert calls; a sinon-chai plugin exists for Chai, you may want to have a look at it.

There are many cool other aspects of Mocha, Chai and Sinon I couldn’t cover in this blog post, but I hope it opened your appetite for investigating more about them. Happy testing!

Set up Continuous Integration and Deployment for your JavaScript projects. The Codeship supports GitHub and BitBucket projects and about any techstack you can imagine.

We want to thank Nicolas for granting us permission to republish his original blog post. If you have any questions please let us know in the comments.

Read the original blog entry...

More Stories By Manuel Weiss

I am the cofounder of Codeship – a hosted Continuous Integration and Deployment platform for web applications. On the Codeship blog we love to write about Software Testing, Continuos Integration and Deployment. Also check out our weekly screencast series 'Testing Tuesday'!

@ThingsExpo Stories
SYS-CON Events announced today that AgilePoint, the leading provider of Microsoft-centric Business Process Management software, will exhibit at SYS-CON's 2nd International @ThingsExpo which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. AgilePoint is the leading provider of Microsoft-based Business Process Management (BPM) software products, has 1,300+ on-premise and cloud deployments in 25+ countries and provides the same advanced BPM feature set as J2EE vendors like IBM and Appian for the Microsoft .NET native environment. AgilePoint customer...
The Internet of Things (IoT) promises to evolve the way the world does business; however, understanding how to apply it to your company can be a mystery. Most people struggle with understanding the potential business uses or tend to get caught up in the technology, resulting in solutions that fail to meet even minimum business goals. In his session at Internet of @ThingsExpo, Jesse Shiah, CEO / President / Co-Founder of AgilePoint Inc., will show what is needed to leverage the IoT to transform your business. He will discuss opportunities and challenges ahead for the IoT from a market and tec...
SYS-CON Events announced today that Utimaco will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Utimaco is a leading manufacturer of hardware based security solutions that provide the root of trust to keep cryptographic keys safe, secure critical digital infrastructures and protect high value data assets. Only Utimaco delivers a general-purpose hardware security module (HSM) as a customizable platform to easily integrate into existing software solutions, embed business logic and build s...
One of the biggest challenges when developing connected devices is identifying user value and delivering it through successful user experiences. In his session at Internet of @ThingsExpo, Mike Kuniavsky, Principal Scientist, Innovation Services at PARC, will describe an IoT-specific approach to user experience design that combines approaches from interaction design, industrial design and service design to create experiences that go beyond simple connected gadgets to create lasting, multi-device experiences grounded in people’s real needs and desires.
Samsung VP Jacopo Lenzi, who headed the company's recent SmartThings acquisition under the auspices of Samsung's Open Innovaction Center (OIC), answered a few questions we had about the deal. This interview was in conjunction with our interview with SmartThings CEO Alex Hawkinson. IoT Journal: SmartThings was developed in an open, standards-agnostic platform, and will now be part of Samsung's Open Innovation Center. Can you elaborate on your commitment to keep the platform open? Jacopo Lenzi: Samsung recognizes that true, accelerated innovation cannot be driven from one source, but requires a...
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at Internet of @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, will discuss how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money! Speaker Bio: Esmeralda Swartz, CMO of MetraTech, has spent 16 years as a marketing, product management, and busin...
SYS-CON Events announced today that TeleStax, the main sponsor of Mobicents, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. TeleStax provides Open Source Communications software and services that facilitate the shift from legacy SS7 based IN networks to IP based LTE and IMS networks hosted on private (on-premise), hybrid or public clouds. TeleStax products include Restcomm, JSLEE, SMSC Gateway, USSD Gateway, SS7 Resource Adaptors, SIP Servlets, Rich Multimedia Services, Presence Services/RCS, Diame...
Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, will address the big issues involving these technologies and, more important, the results they will achieve. How important are public, private, and hybrid cloud to the enterprise? How does one define Big Data? And how is the IoT tying all this together?
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
SYS-CON Events announces a new pavilion on the Cloud Expo floor where WebRTC converges with the Internet of Things. Pavilion will showcase WebRTC and the Internet of Things. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices--computers, smartphones, tablets, and sensors – connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades.
The only place to be June 9-11 is Cloud Expo & @ThingsExpo 2015 East at the Javits Center in New York City. Join us there as delegates from all over the world come to listen to and engage with speakers & sponsors from the leading Cloud Computing, IoT & Big Data companies. Cloud Expo & @ThingsExpo are the leading events covering the booming market of Cloud Computing, IoT & Big Data for the enterprise. Speakers from all over the world will be hand-picked for their ability to explore the economic strategies that utility/cloud computing provides. Whether public, private, or in a hybrid form, clo...
SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual Controller™ Technology (SVCT) to eliminate the I/O blender effect and accelerate applications Gridsto...
SYS-CON Events announced today that Red Hat, the world's leading provider of open source solutions, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Red Hat is the world's leading provider of open source software solutions, using a community-powered approach to reliable and high-performing cloud, Linux, middleware, storage and virtualization technologies. Red Hat also offers award-winning support, training, and consulting services. As the connective hub in a global network of enterprises, partners, a...
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at Internet of @ThingsExpo, Andrew Bolwell, Director of Innovation for HP’s Printing and Personal Systems Group, will discuss how key attributes of mobile technology – touch input, senso...
The Internet of Things (IoT) is making everything it touches smarter – smart devices, smart cars and smart cities. And lucky us, we’re just beginning to reap the benefits as we work toward a networked society. However, this technology-driven innovation is impacting more than just individuals. The IoT has an environmental impact as well, which brings us to the theme of this month’s #IoTuesday Twitter chat. The ability to remove inefficiencies through connected objects is driving change throughout every sector, including waste management. BigBelly Solar, located just outside of Boston, is trans...
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, will examine three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics...
Internet of @ThingsExpo Silicon Valley announced on Thursday its first 12 all-star speakers and sessions for its upcoming event, which will take place November 4-6, 2014, at the Santa Clara Convention Center in California. @ThingsExpo, the first and largest IoT event in the world, debuted at the Javits Center in New York City in June 10-12, 2014 with over 6,000 delegates attending the conference. Among the first 12 announced world class speakers, IBM will present two highly popular IoT sessions, which will take place November 4-6, 2014 at the Santa Clara Convention Center in Santa Clara, Calif...
From a software development perspective IoT is about programming "things," about connecting them with each other or integrating them with existing applications. In his session at @ThingsExpo, Yakov Fain, co-founder of Farata Systems and SuranceBay, will show you how small IoT-enabled devices from multiple manufacturers can be integrated into the workflow of an enterprise application. This is a practical demo of building a framework and components in HTML/Java/Mobile technologies to serve as a platform that can integrate new devices as they become available on the market.
SYS-CON Events announced today that O'Reilly Media has been named “Media Sponsor” of SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. O'Reilly Media spreads the knowledge of innovators through its books, online services, magazines, and conferences. Since 1978, O'Reilly Media has been a chronicler and catalyst of cutting-edge development, homing in on the technology trends that really matter and spurring their adoption by amplifying "faint signals" from the alpha geeks who are creating the future. An...
SYS-CON Events announced today that Aria Systems, the recurring revenue expert, has been named "Bronze Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Aria Systems helps leading businesses connect their customers with the products and services they love. Industry leaders like Pitney Bowes, Experian, AAA NCNU, VMware, HootSuite and many others choose Aria to power their recurring revenue business and deliver exceptional experiences to their customers.