No amount of testing will save a large program with a dogshit architecture. Roughly, this is because tests increase coverage linearly with the number of tests, but weird interactions increase exponentially with code size.

This might be fine if you're building a tiny app, or if you're building a medium-sized app that follows a strict existing architecture (like a web app consisting mostly of forms). In which case, have fun.

But if you're building something slightly novel and interesting, then Claude is surprisingly bad at architecture and taste, and it tends to "fix" problems by spewing more slop. What you need instead is actual insight that leads to simplifying principles. This, in turn, allows breaking up the exponential complexity into disciplined patterns. This allows your code complexity to scale far more slowly, allowing an essentially linear number of tests to provide coverage.

I actually download and try people's vibe-coded developer tools. And frankly, those tools are some of the worst software I've used in my life, worse than even Unix-vendor Motif implementations from the early 90s.

Like, I'm super happy that people can vibe-code themselves simple, one-off personal tools. That's incredibly empowering. But that doesn't mean you can big, novel stuff the same way without a competent human actively in the loop.