[zmmmmm]

I think it's just a broader definition of "know how to do". If you can write a test for it then I'm going to argue you know "how" to do it in a bigger picture sense. As in, you understand the requirements and inherent underlying technical challenges behind what you are asking to be done.

The issue is, there are always subtle aspects to problems that most developers only know by instinct. Like, "how is it doing the unicode conversion here" or "what about the case when the buffer is exactly the same size as the message, is there room for the terminating character?". You need the instincts for these to properly construct tests and review the code it did. If you do have those instincts, I argue you could write the code, it's just a lot of effort. But if you don't, I will argue you can't test it either and can't use LLMs to produce (at least) professional level code.