Monday, 17 May 2010

Safe habits

When I was growing up, I found some of my parents' habits irritatingly conservative. Examples included:
  • Always lock doors from the outside using the key
  • Always turn on the cold tap before the hot tap
The idea was that following these habits guaranteed you could never burn yourself or lock yourself out. But I found these precautions frustrating because I knew that it was unlikely that I'd forget my keys or put my hand in the scalding water.

However, I was mistaking the most likely outcome for the entire distribution. In Life's Grandeur, Stephen Jay Gould calls this "reification" - fixating on the average case and ignoring variation and atypical outcomes.

On any given occasion, my cavalier attitude would probably suffice. But sooner or later, if I locked doors by setting the snib and pulling them shut, my keys would not be in my pocket.

My parents understood my fallibility better than I did. And they were in a better position to appreciate the myriad of door-locking scenarios that would confront me over my lifetime.

That's why I like to think that if my mother were a programmer (and she'd make a good one) she would advocate TDD, which goes as follows:
  1. Write a failing test
  2. Write the minimum of code to pass the test
  3. Refactor
If you make TDD a permanent habit then you are inevitably at most 5 or 10 minutes away from working, tested code. And you know that every bit of code you write has a corresponding test.

Be mindful of your development habits, and design them for the bad days, not the average days.