Some parts of a game are easy to test in an automated way (logic, maths, input handling); but there's also a lot that's purely visual and not easily testable.
I would be surprised if the games industry left all of this to manual testing; there's enough money in it that I would guess that effort has been put into being able to regression test at least some visual aspect of games.
Is this true? If so, what are the possible ways that rendering of games can be tested? Capturing output and comparing images (can this be reliable?)? Intercepting data from the graphics card at a low level? Capturing vertex information (etc.) on its way to the graphics card? It seems like there are lots of possibilities; but I can't find any information on this :(
Note: This question was marked as a dupe of this one, but I'm not asking about specific tech/frameworks/tools on how to do this, but more broadly the ideas around this practice, and what the actual games industry do (if they do at all).