When do you start testing?

Although I love TDD, I don’t always use it for everything. I wrote a Python script the other day to clean up my music collection, and I didn’t write any tests for it.

Someone asked me, what’s the trade-off? At what point do you start writing tests?

For me, it’s at one of a few points:

• Somewhere between 100-200 lines of code I start feeling the need for tests
• When I start feeling unclear in my head, I reach to tests to make them clear
• If someone wants to work with me, tests instantly become mandatory
• When I come back to some code after a while
• When I notice my first bug