Remember, it doesn't matter if you've survived 100 Chernobyls, 50 Tsunamis or 20 Covids, all it takes is one bad one to wipe you out of the gene pool(kill). The worse is called worse precisely because it did not happen until then. Yes, testing helps but only when you know what to test, a hastily designed system where the workers are put under pressure and made to ssh into a fleet(See: https://twitter.com/atomicthumbs/status/1032939617404645376) to fix bugs, is not a mere matter of testing. It is a matter of culture, autonomy, prudence, care, and add other things that would help build a well-designed system from ground up.