If services are provisioned by programs, then we can - and should - test those programs. Further, we can write them in a test-driven style: start with the description of how the service should behave, and write a test that expresses this. Then write code that makes that test pass.
Nelson-Smith argues that this and other techniques from the school of Agile software development are of great benefit to systems administrators building modern automated infrastructures. -- John Arundel
The general message of this book is similar to what I'd heard in the Agile community when I attended Agile 2011. The software development community has made incredible and innovative strides in process improvement, but now it's time to spread that innovation to other occupations. The ops team, which the developers have to deal with regularly, are first on the list.