Add project files.

UnitTestApp1/UnitTestApp.xaml.cs

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+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Controls.Primitives;
+using Microsoft.UI.Xaml.Data;
+using Microsoft.UI.Xaml.Input;
+using Microsoft.UI.Xaml.Media;
+using Microsoft.UI.Xaml.Navigation;
+using Microsoft.UI.Xaml.Shapes;
+using Microsoft.VisualStudio.TestTools.UnitTesting.AppContainer;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices.WindowsRuntime;
+using Windows.ApplicationModel;
+using Windows.ApplicationModel.Activation;
+using Windows.Foundation;
+using Windows.Foundation.Collections;
+
+// To learn more about WinUI, the WinUI project structure,
+// and more about our project templates, see: http://aka.ms/winui-project-info.
+
+namespace UnitTestApp1
+{
+    /// <summary>
+    /// Provides application-specific behavior to supplement the default Application class.
+    /// </summary>
+    public partial class UnitTestApp : Application
+    {
+        private Window? _window;
+
+        /// <summary>
+        /// Initializes the singleton application object.  This is the first line of authored code
+        /// executed, and as such is the logical equivalent of main() or WinMain().
+        /// </summary>
+        public UnitTestApp()
+        {
+            InitializeComponent();
+        }
+
+        /// <summary>
+        /// Invoked when the application is launched.
+        /// </summary>
+        /// <param name="args">Details about the launch request and process.</param>
+        protected override void OnLaunched(Microsoft.UI.Xaml.LaunchActivatedEventArgs args)
+        {
+            Microsoft.VisualStudio.TestPlatform.TestExecutor.UnitTestClient.CreateDefaultUI();
+
+            _window = new UnitTestAppWindow();
+            _window.Activate();
+
+            UITestMethodAttribute.DispatcherQueue = _window.DispatcherQueue;
+
+            Microsoft.VisualStudio.TestPlatform.TestExecutor.UnitTestClient.Run(Environment.CommandLine);
+        }
+    }
+}