Add WindowOrder_Owned_Window_Stays_InFront_Of_Topmost_Owner integration test

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

samples/IntegrationTestApp/TopmostWindowTest.axaml

@@ -9,8 +9,10 @@
         Height="480">
   <Grid>
     <TextBox Name="CurrentPosition"
-             Grid.Column="1"
+             VerticalAlignment="Top"
-             Grid.Row="3"
+             IsReadOnly="True" />
+    <TextBox Name="CurrentOrder"
+             VerticalAlignment="Bottom"
              IsReadOnly="True" />
     <Button HorizontalAlignment="Center" Name="MoveButton" VerticalAlignment="Center" Click="Button_OnClick">Move</Button>
   </Grid>

samples/IntegrationTestApp/TopmostWindowTest.axaml.cs

@@ -1,16 +1,39 @@
+using System;
+using System.Runtime.InteropServices;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Interactivity;
+using Avalonia.Threading;
 
 namespace IntegrationTestApp;
 
 public partial class TopmostWindowTest : Window
 {
+    private readonly DispatcherTimer? _timer;
+
     public TopmostWindowTest(string name)
     {
         Name = name;
         InitializeComponent();
         PositionChanged += (s, e) => CurrentPosition.Text = $"{Position}";
+
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+        {
+            _timer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(250) };
+            _timer.Tick += TimerOnTick;
+            _timer.Start();
+        }
+    }
+
+    protected override void OnClosed(EventArgs e)
+    {
+        base.OnClosed(e);
+        _timer?.Stop();
+    }
+
+    private void TimerOnTick(object? sender, EventArgs e)
+    {
+        CurrentOrder.Text = MacOSIntegration.GetOrderedIndex(this).ToString();
     }
 
     private void Button_OnClick(object? sender, RoutedEventArgs e)

tests/Avalonia.IntegrationTests.Appium/WindowTests_MacOS.cs

@@ -202,6 +202,30 @@ namespace Avalonia.IntegrationTests.Appium
             }
         }
 
+        [PlatformFact(TestPlatforms.MacOS)]
+        public void WindowOrder_Owned_Window_Stays_InFront_Of_Topmost_Owner()
+        {
+            Session.FindElementByAccessibilityId("ShowTopmostWindow").Click();
+
+            try
+            {
+                Thread.Sleep(1000);
+
+                var ownerWindowIndex = GetWindowOrder("OwnerWindow");
+                var ownedWindowIndex = GetWindowOrder("OwnedWindow");
+
+                // orderedIndex counts from the front, so the owned window needs the lower index.
+                Assert.True(ownedWindowIndex < ownerWindowIndex,
+                    $"Expected the owned window in front of its topmost owner, but the owner was at " +
+                    $"{ownerWindowIndex} and the owned window at {ownedWindowIndex}.");
+            }
+            finally
+            {
+                CloseWindow("OwnedWindow");
+                CloseWindow("OwnerWindow");
+            }
+        }
+
         [PlatformFact(TestPlatforms.MacOS)]
         public void WindowOrder_Owned_Is_Correct_After_Closing_Window()
         {
@@ -441,6 +465,12 @@ namespace Avalonia.IntegrationTests.Appium
             return int.Parse(order.Text);
         }
 
+        private void CloseWindow(string identifier)
+        {
+            GetWindow(identifier).FindElementByAccessibilityId("_XCUI:CloseWindow").Click();
+            Thread.Sleep(1000);
+        }
+
         public enum ShowWindowMode
         {
             NonOwned,