Just to give you some perspective: my current employer's main product isn't called a game, but it has an engine at its core that is a game engine in all aspect

Just to give you some perspective: my current employer's main product isn't called a game, but it has an engine at its core that is a game engine in all aspect except its name. And we test the sh*t out of it. We have thousands of automated and very sensitive tests on that stuff. Our test suite goes as far as testing for pixel perfect output. And this involves stuff that is "random". It took us some effort to be random in a perfectly reproduceable way, but we got there. Game QA is more involved than that, of course. Content needs to go through a signoff and QA process that involves humans (we do that, too).