In modern web frameworks, it's easy to extend model and controller objects over and over again, leaving you with huge, unwieldy objects. To avoid this, you can extract small pieces into their own classes. This has many benefits, such as: much faster test execution, naming concepts in the system that were previously implicit, and adding explicit abstraction layers. We'll look at an example from Destroy All Software itself, a Rails app, and pull a piece of model logic embedded in a controller out into its own class with isolated tests.