Since WikibaseCirrusSearch depends on CirrusSearch, changes in CirrusSearch may break tests there (or even, in worst cases, actual functionality). However, right now we are not testing WikibaseCirrusSearch and other dependant extensions when we're merging patches into CirrusSearch. This leads to problems like T221111 where some cleanup in CirrusSearch may break WikibaseCirrusSearch, which in turn blocks other extensions.
So, we may want to add WikibaseCirrusSearch and probably also WikibaseLexemeCirrusSearch and WikibaseMediaInfo to tests being run by CirrusSearch. We'd need also to include Wikibase, though I am not sure we need to run Wikibase tests, but it wouldn't hurt probably.