In this chapter, we took a look at how to implement the model layer of our app using TDD. We followed the TDD workflow (red, green, and refactor) to guide the implementation of the required micro features.

We implemented two model structs and a manager class. We added conformance to the Equatable protocol for the model structs in order to make sure that the same to-do item cannot be added to the list more than once. We also encapsulated the internals of the manager class with methods to add, receive, and remove to-do items from the manager.

TDD lead us to a clean, simple, and fully tested model.

In the next chapter, we will implement the controller layer and the view layer of the Model-View-Controller design pattern using TDD.