I recently listened to this episode from the Claude Code creator (here is the video version: https://www.youtube.com/watch?v=PQU9o_5rHC4) and it sounded like their development process was somewhat similar - he said something like their entire codebase has 100% churn every 6 months. But I would assume they have a more professional software delivery process.

I would (incorrectly) assume that a product like this would be heavily tested via AI - why not? AI should be writing all the code, so why would the humans not invest in and require extreme levels of testing since AI is really good at that?

I've gotta say, it shows. Claude Code has a lot of stupid regressions on a regular basis, shit that the most basic test harness should catch.

I mean, I'm slowly trying to learn lightweight formal methods (i.e. what stuff like Alloy or Quint do), behavior driven development, more advanced testing systems for UIs, red-green TDD, etc, which I never bothered to learn as much before, precisely because they can handle the boilerplate aspects of these things, so I can focus on specifying the core features or properties I need for the system, or thinking through the behavior, information flow, and architecture of the system, and it can translate that into machine-verifiable stuff, so that my code is more reliable! I'm very early on that path, though. It's hard!