I've unit tested the core domain of puzzle games and rpg games before. It's like testing business code. It's uniquely suited to that. But they can't tell you if some visual thing looks strange.

It seems like testing in games is a huge problem, in that game QA testing is a big industry. I bet puzzle games and rpg games could gain a huge competitive advantage by testing their core domain. If they're long lasting games with lots of changes coming up.