In Zend Framework 1, it was difficult to follow best practices when it came to writing testable code. Sure, you could make testable models, but once you need those models in a controller, what do you do? Zend Framework 2 makes it much easier. In this post, I'll cover the basics of injecting a model into a controller. The main goal here is to be able to wire up and configure your application from the highest level possible. Constructor injection + inversion of control makes it easy to determine which classes are dependent on other classes.
He creates a "Building" module and a "BuildingController" inside of it. This controller takes in an instance of a "Building" model as a dependency. He also shows how to define this dependency in the "getControllerConfig" method of your module to make it work automatically. He makes the "Building" model itself with no dependencies and sets it up as an "invokable" in that same "getControllerConfig" method.