They generally move at a pretty fast pace and change often(due to the iterative nature of what's "fun"). I don't think I saw a single unit test until I was well out of the game industry.
Their blog regularly goes into details about how it all works. It's very much worth reading.
It's been a few years but if I recall correctly we did have a "smoke test" running on a jenkins box under someone's desk that booted a few levels with most of the game entities(they were called danger_room_1/2/3/etc) and verified that the game didn't crash. Aside from that though there wasn't much else which lead to some spectacular build breaks.
Ah the joys of "AAA" development.