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Manual:PHP unit testing/Writing unit tests

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General advice[edit]

The PHPUnit Manual provides good instructions for understanding and developing unit tests. Pay particularly close attention to the sections on writing and organizing tests.

Developing best practices[edit]

Developers new to unit testing in MediaWiki should use SampleTest.php as a starting point – it contains helpful comments that will ease the process of learning to write unit tests.

Another resource is the slides from the PHPUnit Best Practices talk that Sebastian Bergmann gave at OSCON 2010.

Developers should avoid inventing new conventions or borrowing conventions from other frameworks; using the already well-established PHPUnit conventions will serve to make MediaWiki's tests both useful and usable.

Unit tests should follow A Set of Unit Testing Rules by Michael Feathers.

Write testable code[edit]

Please try to write testable code.

MediaWiki was not written with the objective of being testable. It uses global variables all over the place and static methods in many places. This is a legacy that we have to accept, but try not to introduce these things into new code, and try to change going forward.

A good resource might be Miško Hevery's Guide to Testability. (Miško Hevery is [one of?] Google's Agile Coaches.)

Test conventions[edit]

The filename must end with Test.php. Use SampleTest.php as a starting point.

setUp() and tearDown()[edit]

  • Must be protected functions.
  • tearDown() should be in the opposite order of setUp().
  • setUp() starts with calling its parent.
  • tearDown() ends with calling its parent.

Assertion functions[edit]

  • Must be public functions.
  • The name of the function should be in lowerCamelCase and begin with the word test; e.g., function testFooBar.
  • Whenever possible, refer to the most important method being tested; e.g., Html::expandAttributes is tested in HtmlTest::testExpandAttributes.

Data providers[edit]

  • Must be public functions.
  • The name of the data provider should be in lowerCamelCase and begin with the word provide; e.g., provideHtml5InputTypes.
  • Should not instantiate MediaWiki Services, since data providers are called before setUpBeforeClass. For example, instead of Title::newFromText, use new TitleValue to avoid creating a TitleParser.

Telling a story[edit]

Test output should tell a story. The --testdox output format is a good way to view this story: a test suite execution is displayed as a set of statements about the test classes, along with whether or not they have passed. The statements (unless customized) are the test method names with corrected capitalization and spacing.

The @testdox annotation can be used to customize the message that is displayed. It is not currently used in the MediaWiki codebase.

See "Other Uses for Tests" for more information.

Number of assertions[edit]

Only one assertion per test unless there is a good reason (expensive tests may need to be grouped).


Usually tests code shouldn't do die("Error"), but use the phpunit fail method:

$this->fail( 'A useful error message' )

This would show up as a failure in the testing summary rather than bringing the whole test suite down.

Specific to MediaWiki[edit]

Grouping tests[edit]

PHPUnit allows tests to be put into arbitrary groups. Groups of tests can be selected for execution or excluded from execution when the test suite is run (see the @group annotation, The Command-Line Test Runner and XML Configuration File documentation in the PHPUnit manual for additional details.)

To add a test (or class) to a group, use the @group annotation in the docblock preceding the code. For example:

 * @group Broken
 * @group Internationalization
class HttpTest extends MediaWikiTestCase {

Several functional groups are currently used in MediaWiki unit tests:

  • API - Tests that exercise the MediaWiki API.
  • Broken - Put broken tests into group Broken. Tests in this group will not be run (as is configured in tests/phpunit/suite.xml).
  • Database - Tests that require database connectivity should be put into group Database.
This causes temporary tables to be overlayed over the real wiki database, so test cases can perform database operations without changing the actual wiki.
  • Destructive - Tests that alter or destroy data should be put into group Destructive.
  • Search - Tests that use MediaWiki's built-in search put into group Search.
  • SeleniumFramework - Tests that require SeleniumFramework to be installed should be put in group SeleniumFramework.
  • Stub - Put test stubs into group Stub. Tests in this group will not be run (as is configured in tests/phpunit/suite.xml).
  • Sqlite - Tests that use SQLite should be put into group Sqlite.
  • Standalone - Very slow tests that should not be run in the gate, to help keep tests fast for other gated extensions.
  • Upload - Tests that upload files should be put into group Upload.
  • Utility - Currently unused by any test. Tests in this group will be not be run (as is configured in tests/phpunit/suite.xml).

In addition, tests may also be grouped based on development team:

  • Fundraising
  • EditorEngagement
  • Internationalization
  • etc.

To test only a particular group, use the --group flag from the command line:

composer phpunit:entrypoint -- --group Search

or if you use the Makefile in core/tests/phpunit:

make FLAGS="--group Search" target

where target can be phpunit, safe, etc.


The PHPUnit documentation has a chapter about coverage. There is a coverage report for MediaWiki core generated twice a day. As the forceCoversAnnotation option should be in effect the test should be marked with @covers annotations to express which parts of the code the test actually checks (as opposed to code that is just run but whose results are never tested for with assertions).

Note that @covers requires fully-qualified class names (unlike Doxygen annotations such as @param).


You will want to extend one of the MediaWiki test classes.

class HttpTest extends MediaWikiTestCase {

The following are some common MediaWiki test classes to extend. Bullets at a lower level extend their parent.

  • TestCase - PHPUnit's test class
    • MediaWikiUnitTestCase - For unit tests of methods with no dependencies, or methods whose dependencies are completely mocked. These should go in their own subfolder called /unit/, so that phpunit:unit works correctly.
      • HookRunnerTestBase - Tests that all arguments passed into a HookRunner class are passed along to a HookContainer.
    • MediaWikiIntegrationTestCase - Assists with testing classes that access global variables, methods, services, or a storage backend. Prevents sending actual emails. These should go in their own subfolder called /integration/, so that phpunit:integration works correctly. Can safely test the SQL database if you add @group Database to your tests. Changes to database data are reset at the beginning of each test method.
      • MediaWikiLangTestCase - Does some language setup such as $this->setUserLang( 'en' ); and $this->setContentLang( 'en' ); and does $services->getMessageCache()->disable()
        • ApiTestCase - Has some extra methods for testing the Action API , such as doApiRequest(), doApiRequestWithToken(), buildFauxRequest(), etc.
      • MaintenanceBaseTestCase - For testing MediaWiki maintenance classes.
      • SpecialPageTestBase - For testing MediaWiki special pages.


When testing database-dependent code, you should put your test case in the Database group (see above). That tells MediaWikiTestCase to setup a DB_PRIMARY database connection for you to use in $this->db. Normally, this uses a separate temporary database, with certain limited data prefilled by addCoreDBData, including a 'UTSysop' user and a 'UTPage' title. (The temporary database is created with CREATE TEMPORARY TABLE, and the tables are prefixed with unittest_.) You can force PHPUnit to not use temporary tables (for example, if you want to step debug and look in the database using a database viewer) by setting the .env variable PHPUNIT_USE_NORMAL_TABLES=1. A test case can add additional data to the database by overriding addDBData (which by default does nothing).

Please note that only the table schema is copied over from your actual database, not the existing data in that table.

You can directly test the current contents of the database with assertSelect().

	'test', // Table
	[ 'first_name', 'last_name', 'street' ], // Fields to select
	[], // Conditions
	[ [ 'Jane', 'Doe', 'Broadway' ] ] // Expected values

Here are some examples from extensions that you can look at for reference:

Tests that are not in the Database group still run against a temporary cloned database (even if they ignore $this->db and instead use e.g. wfGetDB() directly); however, this database is only set up once for the whole test run, and not reset between test runs. Tests should avoid relying on this safety feature if possible.

Maintenance scripts[edit]

Test cases for maintenance scripts should inherit from MediaWiki\Tests\Maintenance\MaintenanceBaseTestCase, to handle the different output channels used by maintenance scripts.

The base test case setUp() method will instantiate your Maintenance object for you, if you specify the class to construct by providing the mandatory getMaintenanceClass() in your subclass:

    public function getMaintenanceClass() {
        return PurgeScoreCache::class;

In the unlikely event that you want to do something special to instantiate the class under test, you can override the createMaintenance() method, but hopefully this isn't needed.

By default, the maintenance script output will be suppressed and ignored. If you wish to test output (this is a good idea), use code like:

use MediaWiki\Tests\Maintenance\MaintenanceBaseTestCase;

class PurgeScoreCacheTest extends MaintenanceBaseTestCase {
    public function testNotAThing() {
        $this->maintenance->loadWithArgv( [ '--model', 'not_a_thing' ] );

        $this->expectOutputRegex( '/skipping \'not_a_thing\' model/' );