Fix unit test host crash on iOS 27 by adopting the UIScene life cycle (#25930)

* Fix unit test host crash on iOS 27 by adopting the UIScene life cycle

iOS 27 removed the legacy window life cycle, so the unit test host's plain
UIWindow() crashed at launch with "UIScene life cycle is required for apps
built with this SDK" before the test runner could connect. This blocked every
app-hosted (WordPressTest) suite on iOS 27 while the same binary ran on iOS
26.5.

TestingAppDelegate now opts into the scene life cycle the same way
WordPressAppDelegate does, vending a minimal TestingSceneDelegate that builds
the host window in scene(_:willConnectTo:). The window shows a SwiftUI
"Running unit tests" placeholder. Verified the previously crashing suites pass
on both iOS 27 and iOS 26.5.

* Update mainWindow comment: test host now connects a window scene

The unit test host adopted the UIScene life cycle, so the delegate-window
fallback no longer covers it. Drop the stale claim that the test host never
connects a window scene.

Author: crazytonyli

Modules/Sources/WordPressSharedUI/UIApplication+MainWindow.swift

@@ -2,9 +2,8 @@ import UIKit
 
 public extension UIApplication {
     @objc var mainWindow: UIWindow? {
-        // The delegate-window fallback covers the moments when no scene key window
-        // exists: early in scene connection (before makeKeyAndVisible) and in the unit
-        // test host, which never connects a window scene.
+        // The delegate-window fallback covers the brief moment early in scene
+        // connection, before the scene's key window is made visible.
         connectedScenes
             .compactMap { ($0 as? UIWindowScene)?.keyWindow }
             .first

WordPress/Classes/System/WordPressAppDelegate.swift

@@ -136,8 +136,8 @@ public class WordPressAppDelegate: UIResponder, UIApplicationDelegate {
 
     /// Opts the app into the UIScene life cycle and names the scene delegate in code,
     /// instead of a `UISceneConfigurations` entry duplicated in each target's Info.plist.
-    /// The unit test host runs TestingAppDelegate, which doesn't implement this method,
-    /// so tests keep the legacy life cycle.
+    /// The unit test host (TestingAppDelegate) opts into the scene life cycle the same
+    /// way, because iOS 27 removed the legacy window life cycle.
     public func application(
         _ application: UIApplication,
         configurationForConnecting connectingSceneSession: UISceneSession,

WordPress/Classes/System/main.swift

@@ -1,9 +1,11 @@
 import BuildSettingsKit
 import Foundation
+import SwiftUI
 import UIKit
 
 let isRunningTests = NSClassFromString("XCTestCase") != nil
-let appDelegateClass = isRunningTests ? NSStringFromClass(TestingAppDelegate.self) : NSStringFromClass(WordPressAppDelegate.self)
+let appDelegateClass =
+    isRunningTests ? NSStringFromClass(TestingAppDelegate.self) : NSStringFromClass(WordPressAppDelegate.self)
 
 // The secrets MUST be configured before the app launches.
 //
@@ -20,11 +22,42 @@ UIApplicationMain(
 )
 
 final class TestingAppDelegate: NSObject, UIApplicationDelegate {
+    /// Opt the unit test host into the UIScene life cycle. iOS 27 removed the legacy
+    /// window life cycle, so a plain `UIWindow()` created here crashes the host at launch.
+    /// Mirrors `WordPressAppDelegate`'s programmatic scene opt-in.
+    func application(
+        _ application: UIApplication,
+        configurationForConnecting connectingSceneSession: UISceneSession,
+        options: UIScene.ConnectionOptions
+    ) -> UISceneConfiguration {
+        let configuration = UISceneConfiguration(name: nil, sessionRole: connectingSceneSession.role)
+        if connectingSceneSession.role == .windowApplication {
+            configuration.delegateClass = TestingSceneDelegate.self
+        }
+        return configuration
+    }
+}
+
+final class TestingSceneDelegate: UIResponder, UIWindowSceneDelegate {
     var window: UIWindow?
 
-    func applicationDidFinishLaunching(_ application: UIApplication) {
-        window = UIWindow()
-        window?.rootViewController = UIViewController()
-        window?.makeKeyAndVisible()
+    func scene(
+        _ scene: UIScene,
+        willConnectTo session: UISceneSession,
+        options connectionOptions: UIScene.ConnectionOptions
+    ) {
+        guard let windowScene = scene as? UIWindowScene else {
+            return
+        }
+        let window = UIWindow(windowScene: windowScene)
+        window.rootViewController = UIHostingController(rootView: TestingRootView())
+        window.makeKeyAndVisible()
+        self.window = window
+    }
+}
+
+private struct TestingRootView: View {
+    var body: some View {
+        Text("Running unit tests")
     }
 }