Moved from How to become a MediaWiki hacker:
Testing
When adding features, it's vital to verify you didn't break existing functionality. The usual tool for this is automated testing frameworks. MediaWiki's test suite is still relatively sparse. We have three kinds of tests:
- Parser tests (see tests/parserTests.php), which only test the parser. Try running
php tests/parserTests.php --quick --quietto see how those work. Everything should pass, in theory. You can add new tests or fix existing ones by editing tests/parserTests.txt. - PHPUnit-based unit tests in the tests/phpunit directory. They are typically run through the phpunit.php script invoked from the aforementioned directory. These tests also include ordinary parser tests, though parserTests.php probably works faster. See Manual:PHP unit testing for PHPUnit setup instructions and further details.
- Selenium tests are in directory tests/selenium.
Anyway, if you can't write an automatic test, do manual testing. If you cause breakage too often, people will get annoyed at you, especially if it isn't caught until it goes live on Wikipedia. Revocation of commit access has been threatened in the past occasionally. At the very least, expect serious indignation if you check in syntax errors – try at least loading your wiki, or
php maintenance/checkSyntax.php --modified.