A to-do app needs a model class/struct to store information for to-do items.
We start by adding a new test case to the test target. Open the To-Do project that we have created in the Getting Started with Xcode section of Chapter 2, Planning and Structuring Your Test-Driven iOS App, and select the ToDoTests group. Go to File | New | File..., navigate to iOS | Source | Unit Test Case Class, and click on Next. Put in the name ToDoItemTests, make it a subclass of XCTestCase, select Swift as the language, and click on Next. In the next window, create a new folder, called Model, and click on Create.
Now, delete the ToDoTests.swift template test case.
At the time of writing this chapter, if you delete ToDoTests.swift before you add the first test case in a test target, you will see a pop-up from Xcode telling you that adding the Swift file will create a mixed Swift and Objective-C target:
