I’ve got friends at Boeing on DoD contracts. Not only is it waterfall, it gets tested hardcore. My experience in private industry is the exact opposite. A consultancy I know of just lost (pretty sure) a state contract because they opened shit up to the public because, surprise surprise, they didn’t test their infra changes.

Now I will say that when I have had to manage client SLAs and there is a cost to post-release defects and change requests, testing increases. Not to the level I’m super comfortable with (which is well below perfect, mind you; I like shipping more than once in a lifetime), but a bit more.