That's barely even testing, and it's certainly not TDD. If I play through the feature I just coded or the bug I just fixed, I can verify that it's doing what I

That's barely even testing, and it's certainly not TDD. If I play through the feature I just coded or the bug I just fixed, I can verify that it's doing what I think it's doing, but I need outside verification that it's correct. In effect, I can verify my code's precision (it's doing precisely what I told it to do), but not it's accuracy (if my idea of a feature is inaccurate, my own testing won't catch that). That having been said, TDD and automated testing can definitely make some headway into game development, but there are a whole host of challenges and questions to surmount there, especially for code-bases that are going to get stripped down to bare-bones every 1-3 years for a new game, if they get reused at all, so the tolerance for hacky code is quite a bit higher.