Welcome!

Eclipse Authors: Liz McMillan, Elizabeth White, XebiaLabs Blog, Ken Fogel, Sematext Blog

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
Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportuni...
Smart Cities are here to stay, but for their promise to be delivered, the data they produce must not be put in new siloes. In his session at @ThingsExpo, Mathias Herberts, Co-founder and CTO of Cityzen Data, will deep dive into best practices that will ensure a successful smart city journey.
SYS-CON Events announced today that 910Telecom will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
Pulzze Systems was happy to participate in such a premier event and thankful to be receiving the winning investment and global network support from G-Startup Worldwide. It is an exciting time for Pulzze to showcase the effectiveness of innovative technologies and enable them to make the world smarter and better. The reputable contest is held to identify promising startups around the globe that are assured to change the world through their innovative products and disruptive technologies. There w...
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. 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 - comp...
DevOps at Cloud Expo, taking place Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long dev...
Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, will discuss the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
There is growing need for data-driven applications and the need for digital platforms to build these apps. In his session at 19th Cloud Expo, Muddu Sudhakar, VP and GM of Security & IoT at Splunk, will cover different PaaS solutions and Big Data platforms that are available to build applications. In addition, AI and machine learning are creating new requirements that developers need in the building of next-gen apps. The next-generation digital platforms have some of the past platform needs a...
SYS-CON Events announced today Telecom Reseller has been named “Media Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions wi...
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
Identity is in everything and customers are looking to their providers to ensure the security of their identities, transactions and data. With the increased reliance on cloud-based services, service providers must build security and trust into their offerings, adding value to customers and improving the user experience. Making identity, security and privacy easy for customers provides a unique advantage over the competition.
I wanted to gather all of my Internet of Things (IOT) blogs into a single blog (that I could later use with my University of San Francisco (USF) Big Data “MBA” course). However as I started to pull these blogs together, I realized that my IOT discussion lacked a vision; it lacked an end point towards which an organization could drive their IOT envisioning, proof of value, app dev, data engineering and data science efforts. And I think that the IOT end point is really quite simple…
Personalization has long been the holy grail of marketing. Simply stated, communicate the most relevant offer to the right person and you will increase sales. To achieve this, you must understand the individual. Consequently, digital marketers developed many ways to gather and leverage customer information to deliver targeted experiences. In his session at @ThingsExpo, Lou Casal, Founder and Principal Consultant at Practicala, discussed how the Internet of Things (IoT) has accelerated our abil...
Is the ongoing quest for agility in the data center forcing you to evaluate how to be a part of infrastructure automation efforts? As organizations evolve toward bimodal IT operations, they are embracing new service delivery models and leveraging virtualization to increase infrastructure agility. Therefore, the network must evolve in parallel to become equally agile. Read this essential piece of Gartner research for recommendations on achieving greater agility.
SYS-CON Events announced today that Venafi, the Immune System for the Internet™ and the leading provider of Next Generation Trust Protection, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Venafi is the Immune System for the Internet™ that protects the foundation of all cybersecurity – cryptographic keys and digital certificates – so they can’t be misused by bad guys in attacks...
For basic one-to-one voice or video calling solutions, WebRTC has proven to be a very powerful technology. Although WebRTC’s core functionality is to provide secure, real-time p2p media streaming, leveraging native platform features and server-side components brings up new communication capabilities for web and native mobile applications, allowing for advanced multi-user use cases such as video broadcasting, conferencing, and media recording.