Referring more to smaller places like my own - few hundred employees with ~20 person IT team (~10 developers).
I read enough about testing that it seems industry standard. But whenever I talk to coworkers and my EM, it’s generally, “That would be nice, but it’s not practical for our size and the business would allow us to slow down for that.” We have ~5 manual testers, so things aren’t considered “untested”, but issues still frequently slip through. It’s insurance software so at least bugs aren’t killing people, but our quality still freaks me out a bit.
I try to write automated tests for my own code, since it seems valuable, but I avoid it whenever it’s not straightforward. I’ve read books on testing, but they generally feel like either toy examples or far more effort than my company would be willing to spend. Over time I’m wondering if I’m just overly idealistic, and automated testing is more of a FAANG / bigger company thing.
You should think of an automated test as a specification. If you’ve got the wrong requirements or simply make a mistake while formulating it, then yeah, it can’t protect you from that.
But you’d likely make a similar or worse mistake, if you implemented the production code without a specification.
The advantage of automated tests compared to a specification document, is that you get continuous checks that your production code matches its specification. So, at least it can’t be wrong in that sense.