Like most technical work, it saves money when done well and costs money when done poorly. Most people find themselves somewhere in the middle most of the time so it turns out the discussion is a little more nuanced than that.

Exactly! But it's so much easier to be an unyielding zealot than to think and understand why and if something is working.

As I said above I'm a big advocate of tdd... Do it all the time. So when I say I wouldn't do it for parts of games maybe I have a reason (to gp not you)

Engineers have to do work.. I would unit test core libs... I would also hire manual tester because they were very useful. I'd likely not chase down 100% automated coverage. The goal is to ship a game not have 100% coverage. And I work 100% pure tdd in my day job and side projects so take that for what it's worth.

Only if you intend to change/refactor stuff later. Which in games never happens: engines are mostly thrown out at the end of the game.

Hasn't Gamebryo evolved since the earliest days at Bethesda?