Personally i think the challenge of testing never really changed with AI. You need to know what you want to specifically test before writing/vibe coidng with it. Otherwise it'll just manufacture tests that always passes and are of 0 value.

If some component doest benefit from being extensively tested, then it's still the same today. The difference is now it's so easy to generate something, no matter how useless it is. Worse part is, no one cares. Test passes, it doesn't affect production, line coverage increases, managers think the software is more tested, developers just let a prompt do everything. It's all just testing theatre.

I think E2E is the more important than ever. AI is pretty good at getting the local behaviour correct. So unit tests are of less value. Same can't be said for the system as a whole. The best part is, AI is actually pretty good at writing E2E tests. Ofc, given that you already know what you want to test