About
Exploring Solution Spaces, Keith Ray's blog on Software development and other topics.
Send comments to:
keithray@mac.com
| For Agile Training, eLearning, or Coaching contact: |
| Industrial Logic, Inc. |
| 866-540-8336 (toll free) |
| 510-540-8336 (Berkeley, California) |
| Links |
| xpminifaq |
| Résumé |
| “Adopting XP” Article 2002 (pdf) |
| “ Refactoring” Article 2006 |
| AYE Conference |
| Lucien W. Dupont |
| Elisabeth Hendrickson |
| Johanna Rothman's Managing Product Development |
| Brian Marick's Exploration Through Example |
| Esther Derby's Insights You Can Use |
| Laurent Bossavit's Incipient(thoughts) |
| Dale Emery's Conversations with Dale |
| Martin Fowler's Bliki |
| Creating Passionate Users |
Archives
Subscribe
RSS Exploring Solution Spaces XML
2007.Oct.12 Fri
What's the point of tests that pass all the time?
When I'm doing Test Driven Development, my tests (almost) always fail - at least once.
This is because I write a test and run it before I write the code to make the test pass. It should fail because the functionality isn't implemented yet.
I could design my code without using the tests to guide me, but then I find that I spend a lot of time debugging manually, and afterwards, I don't have tests to find regressions. I define regressions as bugs for already-implemented features which can get injected into the code during refactoring or when adding new features. So the tests in TDD are serving two purposes: guiding my design, and guarding against regressions.
However, I don't check into source-code-control when tests are failing, and I hope my team-mates do the same thing. So from the viewpoint of the team's continuous integration server, the programmer tests used for TDD should never fail.
Sometimes they do, because we make mistakes: we forget to check in something, or the tests are poorly written -- for example, a test might be accessing a live external server that isn't running all the time, or has inconsistent time-outs or other 'flaky' behavior.
The skills for TDD and writing reliable tests are more subtle than they ways of wizards, but they can be learned. [I've been watching Lord of Rings again.]