Lately we are getting some great questions on our Pester issue page, I am reposting soem of my answers as blog posts, because I hope they are worth reading. You can access the original question here.

We test because we need a simple set of boundaries that define a more complicated system. Coming up with simple tests and gradually refining them to define more complex systems is easy for us humans. Definitely easier than defining a complex system in a single swoop.