As engineers and developers, we tend to be passionate about building something great, which Drupal is perfect for doing. We tend to put a high priority on the quality of what it is we’re building. The best way to ensure sustainable quality in what you build is through testing. While Drupal already uses some great tools for this (simpletest, php code sniffer, php unit) I like to talk about another option; Behat, and the Behavior Driven Development paradigm that it encourages. BDD will deliver a better product; something that developers and clients can both agree on.