Remap.js

Remap.js allows you to replace the actual dependencies of a module with your chosen ones. It's a simple but powerful tool to inject mocks for your test suites.

Installing Remap.js

Simply install via bower:

$ bower install remapjs

And include it after including require.js:

<script data-main="scripts/main" src="path/to/require.js"></script>
<script src="path/to/remap.js"></script>

Using Remap.js

When adding remap.js after require.js you get a new method, require.contextualized(dependencyMap) that creates a new version of the require function allowing you to load modules in a regular way but forcing dependencies to follow the dependencyMap you passed as parameter. This is specially useful for unit testing:

var testingSubject;

var req = require.contextualized({
  'ChatServer': ServerMock,
  'ChatClient': ClientMock
});

// When trying to load dependecies for ChatWidget, requiring 'ServerMock' will
// return MockServer and requiring 'ClientMock' will return MockClient.
req('ChatWidget', function (ChatWidget) {
  testingSubject = ChatWidget;
});

Use with Mocha.js

Actually, I did not use require.js for bundling my projects but I find it very convenient for unit testing. This is a setup I usually work with combined with Mocha.

Suppose you have this definition of ChatWidget:

// src/ChatWidget.js

define([
  'ChatServer',
  'ChatClient'
], function (ChatUI, ChatClient) {

  /** My chat widget implementation...*/

  return ChatWidget;
});

And you want ChatWidget to use mocked object instead of the actual modules, so in your spec file you do:

// ChatWidget.spec.js

define([
  'mocks/ServerMock',
  'mocks/ClientMock'
], function (ServerMock, ClientMock) {

  describe(function () {
  
    var ChatWidget;
    
    var req = require.contextualized({
      'ChatServer': ServerMock,
      'ChatClient': ClientMock
    });
  
    beforeEach(function (done) {
      req('src/ChatWidget', function (subject) {
        ChatWidget = subject;
        done();
      });
    });

    // Your tests here...
  
  });

});

Notice you don't load your test subject (ChatWidget) at the beginning of the spec but in the beforeEach() hook, this allow to isolate the module and provide mocks in different ways according to the specific functionality you're testing.

Thanks

The implementation was inspired by Mock/stub your requirejs dependecies.