This is a tracking task; it subtasks are those which identify a unit test in MediaWiki core or one of its extensions to fail or return an error on a *clean installation*.

Clean installation means you followed these steps and got errors/failures:

• Download/clone MediaWiki (specify which version, preferably a git version ID)
• Run composer update
• Run MediaWiki installer (if you modified anything but the mandatory configurations, specify that)
• If testing an extension:
  • Download/clone the extension (specify which version, preferably a git version ID)
  • Run composer update inside extension's directory
  • Install the extension with bare-minimum configurations (often, only a modification of LocalSettings.php and running the maintenance script)
• Run php tests/phpunit/phpunit.php and get errors/failures