Add utility to run UI tests for Screen states, add screen states for template and finish unit test.

RiotSwiftUI/Modules/Common/Mock/MockScreenState.swift

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+// 
+// Copyright 2021 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 SwiftUI
+
+/// Used for mocking top level screens and their various states.
+@available(iOS 14.0, *)
+protocol MockScreenState {
+    static var screenStates: [MockScreenState] { get }
+    var screenType: Any.Type { get }
+    var screenView: AnyView { get }
+    var stateTitle: String { get }
+}
+
+@available(iOS 14.0, *)
+extension MockScreenState {
+    
+    /// Get a list of the screens for every screen state.
+    static var screensViews: [AnyView] {
+        screenStates.map(\.screenView)
+    }
+    
+    /// A unique key to identify each screen state.
+    static var screenStateKeys: [String] {
+        return Array(0..<screenStates.count).map(String.init)
+    }
+    
+    /// Render each of the screen states in a group applying
+    /// any optional environment variables.
+    /// - Parameters:
+    ///   - themeId: id of theme to render the screens with
+    ///   - locale: Locale to render the screens with
+    ///   - sizeCategory: type sizeCategory to render the screens with
+    /// - Returns: The group of screens
+    static func screenGroup(
+        themeId: ThemeIdentifier = .light,
+        locale: Locale = Locale.current,
+        sizeCategory: ContentSizeCategory = ContentSizeCategory.medium
+    ) -> some View {
+        Group {
+            ForEach(0..<screensViews.count) { index in
+                screensViews[index]
+            }
+        }
+        .theme(themeId)
+        .environment(\.locale, locale)
+        .environment(\.sizeCategory, sizeCategory)
+    }
+    
+    /// A title to represent the screen and it's screen state
+    var screenTitle: String {
+        "\(String(describing: screenType.self)): \(stateTitle)"
+    }
+    
+    /// A title to represent this screen state
+    var stateTitle: String {
+        String(describing: self)
+    }
+}
+
+@available(iOS 14.0, *)
+extension MockScreenState where Self: CaseIterable {
+    static var screenStates: [MockScreenState] {
+        return Array(self.allCases)
+    }
+}