I think migrating from prototype to maintenance mode is a continuum. For some reason maintenance mode seems to begin (IMHO) some where around 60%--80% of work

I think migrating from prototype to maintenance mode is a continuum. For some reason maintenance mode seems to begin (IMHO) some where around 60%--80% of work for version 1.0. At that point it's too risky not to be testing routinely and things should have settled enough that you could depend on some solidified interfaces. I like this approach to TDD. This feels more efficient than starting with failed test cases on day 1.