Mark Shuttleworth:

What’s good enough performance? Well, I like to think in terms of “heartbeat time”. If the major operations which I have to do regularly (several times in an hour) take less than a heartbeat, then I don’t ever feel like I’m waiting. Things which happen 3-5 times in a day can take a bit longer, up to a minute, and those fit with regular workbreaks that I would take anyhow to clear my head for the next phase of work, or rest my aching fingers.

Take this rule of thumb and apply it to unit tests:

  • Tests for whatever chunk of code you are working on should take “less than a heartbeat”.
  • Your entire testing suite (that you run 3-5 times in a day, right?) can take longer to run, up to a minute.

Authors of tests and testing frameworks, there’s your challenge.

Tests that take too long to run just won’t get run. Programmers will postpone running the suite until the last possible moment. When using something like PQM or Buildbot, this can be disastrous. Other developers might have to wait hours for their code to land on trunk.

Gerard Mezsaros’s new book, xUnit Test Patterns has some good ideas about what to do and what not to do to make your tests run in a couple of heartbeats.