Setting up a project using karma with mocha and chai

Recently, I was on a quest to evaluate the mocha javascript testing framework
and its direct support for async testing in the browser. I had a hard time finding a complete description of everything that needed to be done in order to get things working with karma for testing in the browser as opposed to testing a node module.

Consequently, I decided it would be useful to create a guide for those who have similar interests to save everyone time. If you want to skip the steps and just download the code, feel free to clone my github repository. As a quick aside, I decided to try mocha thanks to some frustrations with jasmine. Async testing with jasmine can be done, but it does not have first-class support in my opinion. I intend to give buster a spin in the near future as well.

This tutorial assumes that you are on a unix-based system (I used OSX to write the article) and already have a working nodejs and npm installation, therefore installing and configuring a node.js/npm environment is outside the scope of this article. With that said, let’s dig in!

  1. Create a directory to hold the project and navigate to that directory:
    • mkdir <new_dir>
    • cd <new_dir>
  2. We’ll be installing a bunch of npm modules, so let’s run npm init to build our package.json file for us
  3. Let’s install karma with npm. I recommend installing it locally, since it’s likely that you’ll be either executing karma from an IDE (such as webstorm) or as a grunt task. Additionally, one project may be configured for one version of karma while a different project can use a different version if needed.
    • npm install karma --save-dev
    • At the time I wrote this article, the latest stable version of karma was 0.10.8.
  4. Now we’re ready to install mocha:
    • npm install mocha --save-dev
  5. We’ll also need the karma-mocha adapter so we can use mocha as a test framework with karma:
    • npm install karma-mocha --save-dev
  6. An assertion library will need to included as well. I prefer the chai assertion library, since it offers both bdd style assertions using expect and should as well as junit-style assertions.
    • npm install karma-chai --save-dev.
    • Installing chai this way will make it available as a framework within karma, which makes setup much simpler.
  7. I also find sinon to be extremely useful for stubbing and spying, so let’s install it to round out our set of packages required to get our test environment provisioned:
    • npm install karma-sinon --save-dev

At this point, our package.json should have a devDependencies directive that looks something like this:


We can now create our karma configuration and write some tests. Let’s first make sure that our karma installation is working correctly:

  • ./node_modules/karma/bin/karma --version

That should print out the version number to the console if everything is working correctly. If you want to, you can initialize a karma configuration file using:

  • ./node_modules/karma/bin/karma init

I’ll provide the boilerplate so you can avoid that step. Include the following configuration in a file named


Once that file is ready, we can create a failing test to ensure our configuration is working as expected. Create a new file in src/test called test.spec.js. Create the directory:

  • mkdir -p src/test

And a test file with the following contents:

describe("A test suite", function() {
   beforeEach(function() { });
   afterEach(function() { });
   it('should fail', function() { expect(true); });

With our test spec in place, we can run karma and make sure that we can successfully execute failing tests. ./node_modules/karma/bin/karma start karma.conf.js

After running our tests, we should see some output along the lines of

A test suite should fail FAILED

If so, then you’ve successfully configured karma with mocha, chai and sinon. Cheers!

Update: 07/14/14

I recently updated this to use the new 0.12.x version of karma and also added an example Gruntfile.js

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