fix: Correctly run FullWindow tests in context of Uno Island

src/SamplesApp/SamplesApp.Shared/App.xaml.cs

@@ -656,6 +656,10 @@ namespace SamplesApp
 		public void AssertIssue8641NativeOverlayInitialized()
 		{
 #if __SKIA__
+			if (Uno.UI.Xaml.Core.CoreServices.Instance.InitializationType == Uno.UI.Xaml.Core.InitializationType.IslandsOnly)
+			{
+				return;
+			}
 			// Temporarily add a TextBox to the current page's content to verify native overlay is available
 			Frame rootFrame = Windows.UI.Xaml.Window.Current.Content as Frame;
 			var textBox = new TextBox();

src/SamplesApp/SamplesApp.UnitTests.Shared/Controls/UnitTest/UnitTestsControl.cs

@@ -87,6 +87,13 @@ namespace Uno.UI.Samples.Tests
 			Private.Infrastructure.TestServices.WindowHelper.CurrentTestWindow =
 				Windows.UI.Xaml.Window.Current;
 
+			Private.Infrastructure.TestServices.WindowHelper.IsXamlIsland =
+#if HAS_UNO
+				Uno.UI.Xaml.Core.CoreServices.Instance.InitializationType == Xaml.Core.InitializationType.IslandsOnly;
+#else
+				false;
+#endif
+
 			DataContext = null;
 
 			SampleChooserViewModel.Instance.SampleChanging += OnSampleChanging;

src/Uno.UI.RuntimeTests/IntegrationTests/common/TestServices.WindowHelper.cs

@@ -7,6 +7,8 @@ using System.Runtime.CompilerServices;
 using Windows.UI.Xaml.Media;
 using Windows.UI.Xaml.Tests.Enterprise;
 using Windows.UI.Core;
+using Uno.Helpers;
+using MUXControlsTestApp.Utilities;
 #if NETFX_CORE
 using Uno.UI.Extensions;
 #elif __IOS__
@@ -28,6 +30,8 @@ namespace Private.Infrastructure
 
 			public static XamlRoot XamlRoot { get; set; }
 			
+			public static bool IsXamlIsland { get; set; }
+
 			public static Windows.UI.Xaml.Window CurrentTestWindow
 			{
 				get
@@ -46,14 +50,21 @@ namespace Private.Infrastructure
 			public static UIElement WindowContent
 			{
 				get => UseActualWindowRoot
-					? CurrentTestWindow.Content
+					? (IsXamlIsland ? GetXamlIslandRootContentControl().Content as UIElement : CurrentTestWindow.Content)
 					: EmbeddedTestRoot.getContent?.Invoke();
 				internal set
 				{
 					if (UseActualWindowRoot)
+					{
+						if (IsXamlIsland)
+						{
+							GetXamlIslandRootContentControl().Content = value;
+						}
+						else
 						{
 							CurrentTestWindow.Content = value;
 						}
+					}
 					else if (EmbeddedTestRoot.setContent is { } setter)
 					{
 						setter(value);
@@ -65,16 +76,41 @@ namespace Private.Infrastructure
 				}
 			}
 
+			private static ContentControl GetXamlIslandRootContentControl()
+			{
+				var islandContentRoot = EmbeddedTestRoot.control.XamlRoot.Content;
+				if (islandContentRoot is not ContentControl contentControl)
+				{
+					contentControl = VisualTreeUtils.FindVisualChildByType<ContentControl>(islandContentRoot);
+				}
+
+				return contentControl;
+			}
+
 			public static void SaveOriginalWindowContent()
+			{
+				if (IsXamlIsland)
+				{
+					_originalWindowContent = GetXamlIslandRootContentControl().Content as UIElement;
+				}
+				else
 				{
 					_originalWindowContent = CurrentTestWindow.Content;
 				}
+			}
 
 			public static void RestoreOriginalWindowContent()
 			{
 				if (_originalWindowContent != null)
+				{
+					if (IsXamlIsland)
+					{
+						GetXamlIslandRootContentControl().Content = _originalWindowContent;
+					}
+					else
 					{
 						CurrentTestWindow.Content = _originalWindowContent;
+					}
 					_originalWindowContent = null;
 				}
 			}

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_XamlRoot.cs

@@ -12,6 +12,11 @@ namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml
 		[RunsOnUIThread]
 		public async Task When_Loaded_Matches_Window_Root()
 		{
+			if (TestServices.WindowHelper.IsXamlIsland)
+			{
+				return;
+			}
+
 			var border = new Border();
 			var completionSource = new TaskCompletionSource<XamlRoot>();
 			border.Loaded += (s, e) =>