Then I disagree with you
> You still have to have a human who knows the system to validate that the thing that was built matches the intent of the spec.
You don't need a human who knows the system to validate it if you trust the LLM to do the scenario testing correctly. And from my experience, it is very trustable in these aspects.
Can you detail a scenario by which an LLM can get the scenario wrong?
The whole point is that you can't 100% trust the LLM to infer your intent with accuracy from lossy natural language. Having it write tests doesn't change this, it's only asserting that its view of what you want is internally consistent, it is still just as likely to be an incorrect interpretation of your intent.
I do not trust the LLM to do it correctly. We do not have the same experience with them, and should not assume everyone does. To me, your question makes no sense to ask.