Manual:PHP unit testing/Writing unit tests

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

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.

Write Testable Code
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.)

Telling a story
Test output should tell a story (output options). The testdox format enlighten this.

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

Grouping tests
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  annotation in the docblock preceding the code. For example:

""

Eight groups are currently used in the MediaWiki unit tests:
 * 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.
 * Destructive: Tests that alter or destroy data should be put into group Destructive.
 * Fundraising: Tests related to WMF fundraising (CentralNotice, DonationInterface, etc.)
 * 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.
 * 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).

To test only a particular group, use the --group flag from the command line: php phpunit.php --group Search

Developing best practices
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. Pay particularly close attention to the sections in the PHPUnit manual on writing and organizing tests.

Failing
Usually tests code shouldn't do, but throw an exception:

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