Manual:JavaScript unit testing

MediaWiki's QUnit test suite running in Chrome.

MediaWiki uses QUnit to unit test its JavaScript code base.

Run from a browser[edit]

  1. Set $wgEnableJavaScriptTest to true. (This is already set if you use MediaWiki-Docker or MediaWiki-Vagrant.)
  2. Visit Special:JavaScriptTest in a browser to run the tests.

Run from the command line[edit]

One-time setup:

  1. Ensure environment variables MW_SERVER and MW_SCRIPT_PATH are set. Either each time, or from ~/.bash_profile to have them always:
    # Adjust these values for your own environment.
    export MW_SERVER=http://localhost:8080
    export MW_SCRIPT_PATH=/w
  2. Enter an isolated environment where you have Node.js and npm. Why?
    • If using MediaWiki-Docker, consider using Fresh.
      Run fresh-node -net -env from the MediaWiki directory.
    • If using MediaWiki-Vagrant, simply ssh to your Vagrant VM and navigate to the MediaWiki directory.
  3. Once inside your isolated shell, run npm ci to install or update any dependencies.


This runs the QUnit tests in Headless Chrome:

$ npm run qunit
Running "karma:main" (karma) task
 INFO [launcher]: Starting browser ChromeHeadless
     ✔ escapeRegExp
     ✔ debounce

 Finished in 5.42 secs
 ✔ 440 tests completed

You can run QUnit tests for specific components (MediaWiki to run MediaWiki core QUnit tests, or the name of an extension or skin) with the --qunit-component option:

$ node_modules/grunt/bin/grunt qunit --qunit-component=GrowthExperiments
Running "karma:main" (karma) task

INFO [launcher]: Starting browser ChromeHeadless

    ✔ Loader status
    ✔ assert.htmlEqual
    ✔ serializeActionData
    ✔ isUserInVariant
    ✔ getDefaultPanelForSuggestedEditSession for copyedit
    ✔ updateEditMode for link-recommendation
    ✔ updateEditMode for copyedit, isEditing
    ✔ constructor
    ✔ setMessage with currentPosition < totalCount
    ✔ setMessage with currentPosition === totalCount
    ✔ setMessage with currentPosition > totalCount
    ✔ constructor
    ✔ should log impressions
    ✔ should get log metadata
    ✔ getRenderData: target width < original width
    ✔ getRenderData: the image file needs to be re-rasterized
    ✔ getRenderData: vector image
    ✔ getRenderData: target width > original width
    ✔ getRenderData: 3x target width
    ✔ getRenderData: 2.5x target width
    ✔ getRenderData: vertical image with landscape viewport
    ✔ getRenderData: with specified render width

Finished in 0.03 secs

✔ 46 tests completed

How to help?[edit]

Run tests before committing[edit]

Make it a habit to run unit tests before committing and submitting your changes to Gerrit.

Write unit tests[edit]

Always write unit tests for new functionality. We're also looking to expand our unit test coverage of already existing modules in the MediaWiki JavaScript library.

Write a test[edit]

It is the convention to name the test suite file after the module it covers. For example, mediawiki.user.test.js covers the mediawiki.user module.

Inside the test suite should be one, and only one, call to QUnit.module with the module name.

The unit tests for MediaWiki core are located in the tests/qunit/suites/ directory.

Register a test[edit]

MediaWiki core[edit]

Test suites are added to the registration of the mediawiki.tests.qunit.suites module in /tests/qunit/QUnitTestResources.php.

Tests are organised into a directory structure that matches the directory structure of the code being tested. For example: The unit test for resources/mediawiki.util/mediawiki.util.js can be found at tests/qunit/suites/resources/mediawiki.util/mediawiki.util.test.js.


 'mediawiki.tests.qunit.suites' => array(
 	'scripts' => array(
+		'tests/qunit/suites/resources/mediawiki/mediawiki.example.test.js',
 	'dependencies' => array(
+		'mediawiki.example',


Extensions register their QUnit tests via the QUnitTestModule attribute in extension.json.

See also[edit]