[markmaglana]

I tend to go by how much anxiety a piece of code might give me once it goes to production. If I expect the level of anxiety to breach a certain threshold (usually when there’s too many logic branching than I can keep in my head), then I write the tests first.

The above assumes though that I’ve done enough previous discovery to have a relatively robust model of the problem domain. If not, I prototype first and during this stage I won’t be using TDD. Prototypes produced are throwaway, of course.