Based on my experience, it's a rare skill if they can do it well. The problem is everyone says "I do tests"

I have been interviewing candidates regularly for over a decade. What the candidate says on his resume and the actual level of his skill is not at all correlated.

I have met many very good candidates that were obsessively worrying about gaps in their knowledge. At the same time poor candidates seem to be very confident thinking they are master developers but can't solve simplest task on a whiteboard.

Yes, sadly my experience is very similar. The more confident a candidate is, usually the poorer they are.

Yeah sorry, I was just trying to be succinct in the post, I been working on fixing some tests lately so I guess that's why it came to mind.

Good luck to you in your search!

At scale, some companies do employ folks dedicated to producing tests, yes.