A developer is a writer; one writes English and the other writes code, but they both write to a human audience (the only "code" a machine needs to see is 0s and 1s; programming languages are for humans).

So there really shouldn't be a big difference in hiring a writer vs. a developer; and a good test would probably be to have developers write essays in English about a technical question: can they make themselves understood?

I would not hire a developer who is incapable of explaining what he's doing, why he's doing it, what the other options are, etc.

Wouldn't it be a good technique to have interviewees bring an example of their own code that they're especially proud of, and have them explain what it does and why it's great?