Add tests for linking a new device. (#4934)

* Replace GrantLoginWithQrCodeHandlerSDKMock with LinkNewDeviceServiceMock.

Add tests for all initial states on the QRCodeLoginScreen.

* Add tests for linking both mobile and desktop devices.

* Add UI tests for linking a new device.

* Don't show the Link Desktop Computer button when running on macOS.

This mirrors the decision to hide the Sign In With QR Code button on the start screen.

UITests/Sources/LinkNewDeviceTests.swift

@@ -11,16 +11,38 @@ import XCTest
 class LinkNewDeviceTests: XCTestCase {
     enum Step {
         static let selectDevice = 1
+        static let linkMobileDevice = 2
+        static let linkDesktopComputer = 3
         static let dismissed = 99
     }
     
     func testFlow() async throws {
+        // Root screen
         let app = Application.launch(.linkNewDevice)
         try await app.assertScreenshot(step: Step.selectDevice)
         
+        // Link showing a QR code
+        let mobileDeviceButton = app.buttons[A11yIdentifiers.linkNewDeviceScreen.mobileDevice]
+        mobileDeviceButton.tap()
+        try await app.assertScreenshot(step: Step.linkMobileDevice)
+        
+        // Pop back to the root screen
+        let backButton = app.buttons["Link new device"]
+        backButton.tap()
+        try await app.assertScreenshot(step: Step.selectDevice)
+        
+        // Link scanning a QR code
+        let desktopComputerButton = app.buttons[A11yIdentifiers.linkNewDeviceScreen.desktopComputer]
+        desktopComputerButton.tap()
+        try await app.assertScreenshot(step: Step.linkDesktopComputer)
+        
+        // Pop back to the root screen
+        backButton.tap()
+        try await app.assertScreenshot(step: Step.selectDevice)
+        
+        // Dismiss the flow
         let cancelButton = app.buttons[A11yIdentifiers.linkNewDeviceScreen.cancel]
         cancelButton.tap()
-        
         try await app.assertScreenshot(step: Step.dismissed)
     }
 }