As a Ruby developer, we are responsible for providing unit test harness to support our development. Not only it provides a clean code base, but it also allows you to introduce changes as the needs of your application's supported business over time.
Putting the same effort around your application's infrastructure gives the same benefit as well. Being able to support sudden traffic to your application is as important as delivering features to your users. In this talk, I discussed how to treat your Infrastructure as Code with the same test-driven development techniques you do in your application.