A while ago a patch of mine was merged to MW core which broke page moves (see followup Gerrit change 170882). Jenkins greenlighted the original change, because there isn't even a single unit test that tests page moves.
Test coverage of the includes/page directory [1] is pretty woeful in general. Article.php and WikiPage.php in particular are pretty crucial files in the MediaWiki code base; any stuff-ups there are likely to break such basic features as page editing, moves, deletion, etc.
[1] https://integration.wikimedia.org/cover/mediawiki-core/master/php/includes_page.html
Version: unspecified
Severity: enhancement