Here’s the situation:

  • You bundle your app/library with output.libraryTarget = amd (and for the sake of the example let’s say that also output.library = "myLibrary")
  • You want to test it using Mocha
  • You want to run your tests using Karma

I had a few challengues here and I haven’t found any documentation about it so I thought this might be useful to somebody.

You have to use:

  • karma-mocha to run your mocha tests with karma. You can also use whatever test framework they support
  • karma-requirejs to load your amd app, this is key, we’ll see why.

First, the obvious:

npm i -D karma-mocha karma-requirejs

You might need to install other peer dependencies like requirejs and mocha.

In your karma.conf.js:

module.exports = function(config) {
		// add the installed frameworks here
		frameworks: ["mocha", "requirejs"],
		files: [
			//here we include all tests, see the file below
			//this is the file that will require our amd bundle, see the file below
		preprocessors: [
			// preprocess all your tests with webpack, so you bundle all the necessary dependencies
			"src/test/index.js" : ["webpack"]
		// load plugins
		plugins: [

Karma will load (you can see all this if you run the tests with a browser, in the debug.html)

<!-- ... -->
<!-- Dynamically replaced with <script> tags -->
<script type="text/javascript" src="/base/node_modules/requirejs/require.js"></script>
<script type="text/javascript" src="/base/node_modules/karma-requirejs/lib/adapter.js"></script>
<link type="text/css" href="/base/node_modules/mocha/mocha.css" rel="stylesheet">
<script type="text/javascript" src="/base/node_modules/mocha/mocha.js"></script>
<script type="text/javascript" src="/base/node_modules/karma-mocha/lib/adapter.js"></script>
<script type="text/javascript" src="/base/src/test/js/index.js"></script>
<script type="text/javascript" src="/base/src/test/js/runner.js"></script>
<script type="text/javascript">
<!-- ... -->
  1. The karma runner code
  2. requirejs and requirejs-adapter.
  3. mocha and mocha-adapter
  4. Your index.js bundle (as you defined your libraryTarget: amd it will just define your module)
  5. And your runner.js that will require your myLibrary module.
  6. The script that starts the tests, enclosed in a script tag.

It’s important that you use karma-requirejs instead of just requirejs from your bower_components or node_modules, because what you really need is the requirejs-adapter, why?

As the execution of your tests is asynchronous, the call to window.__karma__.loaded() would be done before executing the tests. The requirejs-adapter overrides the __karma__.loaded function to do nothing and waits for your call to window.__karma__.start() (karma’s “loaded()” calls “start()”).



// require all modules ending in "_test" from the
// current directory and all subdirectories
var testsContext = require.context(".", true, /_test$/);

So the runner needs to load your amd library and tell karma to start running the tests!


require(["myLibrary"], function(myLibrary){
	// probably you don't want to do anything with your library here
	// I didn't...
	console.log("Let the tests begin...");
	// now that our bundle with the tests are loaded, run the tests!

This way, your app + tests are loaded and required, and your tests can be ran by karma.

I figured all these out by using these resources:


Hope it helps! Till the next one.

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Tomas Alabes

Software Engineer, author, blogger and obsessive learner, from Argentina living in Silicon Valley



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