[crazygringo]

I used to be like that sometimes. Then I started realizing I'd get the function 90% complete and discover an edge case and have to start over in a way that could handle the edge case. Sometimes this could happen twice.

Documenting your requirements by writing the tests in advance is of course painful because it forces you to think more upfront about the edge cases in advance. But that's precisely why it saves time in the long run, because then it makes it a lot more likely you can write the function correctly from the start.