If you are iterating their isn't always distinct prototypes — just quick first-draft implementations. Sometimes these are good enough. In my experience once ev

If you are iterating their isn't always distinct prototypes — just quick first-draft implementations. Sometimes these are good enough. In my experience once everyone is happy with the way something works then it is sensible to move to lock-down — tests, documentation, performance testing, refactoring. Doing any of those four things is a waste of time and energy until the design is decided upon. In agile development the design is not decided upon before the first code is written. It is always jointly discovered through iteration and discussion between designers, user-testers and developers. If you write your documentation first then I suspect you can get away with writing all your tests first. But that's not a process I would call 'agile' and I doubt it ever results in good software.