We have all done this (includind, I noticed when searching for potential dupes, the people who created the Moodle plugins DB! MDLSITE-1412): We have added a capability (or a cache) and failed to add the requried string.

And, just running the unit tests for one plugin will not catch this (a full unit test run will, via some of the core checks, but that is a very ineffcient wayh to find this.)

Anyway, I suggest adding a new check, but for submissions to Moodle core, and in the plugins DB validation for separate plugins, which goes through the flies like db/access.php and db/caches.php, and verifies that the land strings that should exist because of what are in those files really are present.

Thanks for considering this.