Locking behavior with tests isn't the same as comprehensive and foolproof tests. They might not cover every edge case, but will fail if the happy path starts failing for some reason.

And yes, copy-pasting is a horrendous way to write code, but everyone does it.

When you're adding the 1600th CRUD endpoint of your career to an enterprise Java/C# application, can you with all honesty say you will type every single character with the same thought and consideration every time?

Or do you just make one, copy-paste that one and modify accordingly?

Or if you write 20 unit tests with slight alterations you masterfully craft every single character to perfection?

I have a limited amount of energy to use every day, I choose to use it in places that matter. The hard bits that LLMs and copy-pasting can't speed up.