The purpose of tests is to sell a reliable product instead of crap.
Microsoft traditionally let customers do the testing and they only fix the bugs that will help them separate more people from their money. Heading Styles in Word have been broken since version 1.0. But most people just manually format every line so fixing heading Styles gets hind tit.
Now we have fanatics with hyperthyroid stares who say unit testing every line of code is a point of honor. We have self-evident absurdity like TDD. This shit isn’t helping. These people are passionately moronic.
I write tests for public entrypoints. Period. If they turn up a bug I look at tracelogging to find its actual location. But if people get bugs in unrelated code as a result of changes they’re not doing proper interface/implementation isolation and they should go into another line of work,