> After you prove this feature is a "thing" you want to keep around (and you've nailed down the interface), then it's a perfect time to re-write it with a much higher degree of test coverage.
I find that tests help me write things that are complete and "nailed down" the very first time.
You must have read that with a different definition of "interface" than I did. Under my reading of "user interface", I don't see any way that a developer writing tests has anything to do with how nailed down it is. You need user feedback for that.
I find that tests help me write things that are complete and "nailed down" the very first time.