>which case writing test first hinders productivity.
It kills the flexibility of your code way too early on in development. At best it doubles the inertia preventing any code change. If you know the ideas of "build one to throw away" or "you don't know what you're building until it is built", you understand that you can design as much as you'd like, but at the end of the day, you don't know good your implementation design is until you actually implement. Writing tests first locks you into implementation details before you even use the implementation to know if they're a good idea.
It kills the flexibility of your code way too early on in development. At best it doubles the inertia preventing any code change. If you know the ideas of "build one to throw away" or "you don't know what you're building until it is built", you understand that you can design as much as you'd like, but at the end of the day, you don't know good your implementation design is until you actually implement. Writing tests first locks you into implementation details before you even use the implementation to know if they're a good idea.