To get Karma to run with Require.js we need two files:

• karma.conf.js — which configures Karma
• test-main.js — which configures Require.js for the tests

Let's say our app has a directory structure which looks something like this:

$ tree
.
|-- index.html
|-- karma.conf.js
|-- lib
|   |-- jquery.js
|   |-- require.js
|   `-- underscore.js
|-- src
|   |-- app.js
|   `-- main.js
`-- test
    |-- appSpec.js
    `-- test-main.js
3 directories, 9 files

The first step is creating our karma.conf.js. We can do this in the terminal by running:

$ karma init

This will give you a series of prompts for things such as paths to source and tests and which browsers to capture.

In this example we'll use Jasmine, but other test frameworks works just as well.

Choose "yes" for Require.js.

For the question "Which files do you want to include with <script> tag?", we need to choose all files which are not loaded by Require.js. Usually you'll only need to include your test/test-main.js file, which has the same role for your tests as main.js has for your app when using Require.js.

For the question "Which files do you want to test?", we choose all the files we want to load with Require.js. For this example we'll need:

• lib/**/*.js — all external libraries
• src/**/*.js — our source code
• test/**/*Spec.js — all the tests

And then, for excludes, type src/main.js, as we don't want to actually start the application in our tests.

Now your karma.conf.js should include:

// list of files / patterns to load in the browser
files = [
  JASMINE,
  JASMINE_ADAPTER,
  REQUIRE,
  REQUIRE_ADAPTER,
  {pattern: 'lib/**/*.js', included: false},
  {pattern: 'src/**/*.js', included: false},
  {pattern: 'test/**/*Spec.js', included: false},
  'test/test-main.js'
];
// list of files to exclude
exclude = [
    'src/main.js'
];

Just like any Require.js project, you need a main module to bootstrap your tests. We do this is test/test-main.js.

Karma serves files under the /base directory. So, on the server requests to files will be served up under https://localhost:9876/base/*.

The Require.js config for baseUrl gives a starting context for modules that load with relative paths. When setting this value for the Karma server it will need to start with /base. We want the baseUrl for our tests to be the same folder as the base url we have in src/main.js, so that relative requires in the source won’t need to change. So, as we want our base url to be at src/, we need to write /base/src.

With Karma we don't need to list all test files ourselves as we can easily find them from the files specified in test-main.js: Karma includes all the files in window.__karma__.files, so by filtering this array we find all our test files.

Now we can tell Require.js to load our tests, which must be done asynchronously as dependencies must be fetched before the tests are run. The test/test-main.js file ends up looking like this:

var tests = [];
for (var file in window.__karma__.files) {
    if (/Spec\.js$/.test(file)) {
        tests.push(file);
    }
}
requirejs.config({
    // Karma serves files from '/base'
    baseUrl: '/base/src',
    paths: {
        'jquery': '../lib/jquery',
        'underscore': '../lib/underscore',
    },
    shim: {
        'underscore': {
            exports: '_'
        }
    },
    // ask Require.js to load these files (all our tests)
    deps: tests,
    // start test run, once Require.js is done
    callback: window.__karma__.start
});

Tests can now be written as regular Require.js modules. We wrap everything in define, and inside we can use the regular test methods, such as describe and it. Example:

define(['app', 'jquery', 'underscore'], function(App, $, _) {
    describe('just checking', function() {
        it('works for app', function() {
            var el = $('<div></div>');
            var app = new App(el);
            app.render();
            expect(el.text()).toEqual('require.js up and running');
        });
        it('works for underscore', function() {
            // just checking that _ works
            expect(_.size([1,2,3])).toEqual(3);
        });
    });
});

Install Karma:

$ npm install -g karma

Now we can run the tests with:

$ karma start

If you didn't configure to watch all the files and run tests automatically on any change, you can trigger the tests manually by typing:

$ karma run

Based on Jake Trent's post, with some improvements on shims and so on.