Testing the app's setup

When our app starts, a coordinator should be instantiated and started. This should result in the presentation of the initial view of our app. Follow these steps to refactor the setup from using a storyboard to using a coordinator:

1. Before we can refactor the setup of the app, we need a test that tells us when we break something. Select the ToDoTests group in the project navigator and add a new Unit Test Case Class instance with the name AppSetupTests.
2. Replace the content of the new class with the following:

   // AppSetupTests.swift
   import XCTest
   @testable import ToDo
   class AppSetupTests: XCTestCase {
     func test_application_shouldSetupRoot() {
       let application = UIApplication.shared
       let scene = application.connectedScenes.first
       as? UIWindowScene
       let root =
         scene?.windows.first?.rootViewController
     ...