A distinction on testing that most people don’t realize, from @nelhage:

… for many teams, the purpose of testing is not to find bugs https://blog.nelhage.com/post/two-kinds-of-testing/

The purpose of testing (by which here I mostly mean “CI” in particular) is to serve as a ratchet and as a point of leverage and control for the ever-evolving system that is “the software and the engineers developing it”, and finding net-new bugs is often a distraction and counterproductive to that goal