Add UI tests for AppLockFlowCoordinator. (#2055)

* Add UITests for the App Lock flow.

* Add Notification Signal

Fix unwanted imports in UITests.

ElementX/Sources/UITests/UITestsNotificationCenter.swift

@@ -0,0 +1,57 @@
+//
+// Copyright 2023 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Combine
+import SwiftUI
+
+@MainActor
+/// A notification center that can be injected in the app to post notifications
+/// that are sent from the UI tests runner. Usage:
+/// - Create an instance of the center in the screen you want to test and call `startListening`.
+/// - Create a `UITestSignalling.Client` in the `.tests` mode in your tests.
+/// - Start the app from the tests and call `client.waitForApp()` to establish communication.
+/// - Send the notification from the tests you would like posted in the app.
+class UITestsNotificationCenter: NotificationCenter {
+    private var client: UITestsSignalling.Client?
+    private var signalCancellable: AnyCancellable?
+    
+    /// Starts listening for signals to post notifications.
+    func startListening() throws {
+        let client = try UITestsSignalling.Client(mode: .app)
+        
+        signalCancellable = client.signals.sink { [weak self] signal in
+            Task {
+                do {
+                    try await self?.handleSignal(signal)
+                } catch {
+                    MXLog.error(error.localizedDescription)
+                }
+            }
+        }
+        
+        self.client = client
+    }
+    
+    /// Handles any notification signals, and drops anything else received.
+    private func handleSignal(_ signal: UITestsSignal) async throws {
+        switch signal {
+        case .notification(let name):
+            post(name: name, object: nil)
+        default:
+            break
+        }
+    }
+}