Automated testing gives you the confidence to make very invasive changes to code at any stage during the development process. This is especially important in en

Automated testing gives you the confidence to make very invasive changes to code at any stage during the development process. This is especially important in environments with short iterations, where you are not necessarily designing for features that haven't even been conceived yet. Note that I didn't say unit testing. The author gives the example of writing a test to verify that a bug exists, that the fix makes the test pass, and now as you grow the code you have confidence that the bug doesn't reemerge. The same is true for features. You can write a test that verifies a feature exists, and that the feature continues to exist as you radically refactor the code to make new features fit better, as well as across such dangerous operations as branch merges.