The Standalone PHPUnit test group can be used to “isolate” certain tests, running them in CI only for that extension, but not for other extensions. (See T221434, the test writing manual page, T225184 for an example of moving tests in an extension, and T221434#6053295 for an example of configuring CI accordingly.) We should consider moving some of our slower tests to this group, to speed up CI in other extensions. (This could also include tests in WikibaseLexeme, WikibaseMediaInfo, etc.)

Acceptance criteria🏕️🌟:

• We’ve written an ADR explaining our decision to move tests to the standalone group
• The ADR lists the criteria for choosing specific tests to move (also for future reference); this probably includes “long runtime” and “low risk of breaking due to changes in other extensions”