I have the following rule of thumb: I write the test in the moment when I know for sure how an Interface/Feature should behave. If i know it before the impleme

I have the following rule of thumb: I write the test in the moment when I know for sure how an Interface/Feature should behave. If i know it before the implementation, I write the test first. Most of the time, I start programming and write tests for everything that gets nailed down. If I am in completely new ground, I start playing and do not test beyond "run and see".