Added failing test for #9565.

And another (passing) test for checking that window order is correct when a child window is shown in fullscreen.

samples/IntegrationTestApp/MainWindow.axaml

@@ -17,11 +17,15 @@
       </NativeMenuItem>
       <NativeMenuItem Header="View">
         <NativeMenu/>
-      </NativeMenuItem>  
+      </NativeMenuItem>
     </NativeMenu>
   </NativeMenu.Menu>
   <DockPanel>
     <NativeMenuBar DockPanel.Dock="Top"/>
+    <StackPanel DockPanel.Dock="Bottom" Margin="4" Orientation="Horizontal">
+      <TextBlock Margin="0,0,4,0">WindowState:</TextBlock>
+      <TextBlock Name="WindowState" Text="{Binding WindowState}"/>
+    </StackPanel>
     
     <TabControl TabStripPlacement="Left" Name="MainTabs">
       <TabItem Header="Automation">
@@ -136,6 +140,7 @@
           </ComboBox>
           <Button Name="ShowWindow">Show Window</Button>
           <Button Name="SendToBack">Send to Back</Button>
+          <Button Name="EnterFullscreen">Enter Fullscreen</Button>
           <Button Name="ExitFullscreen">Exit Fullscreen</Button>
           <Button Name="RestoreAll">Restore All</Button>
         </StackPanel>

samples/IntegrationTestApp/MainWindow.axaml.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Avalonia;
@@ -178,6 +179,8 @@ namespace IntegrationTestApp
                 ShowWindow();
             if (source?.Name == "SendToBack")
                 SendToBack();
+            if (source?.Name == "EnterFullscreen")
+                WindowState = WindowState.FullScreen;
             if (source?.Name == "ExitFullscreen")
                 WindowState = WindowState.Normal;
             if (source?.Name == "RestoreAll")

tests/Avalonia.IntegrationTests.Appium/WindowTests_MacOS.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using Avalonia.Controls;
+using Avalonia.Utilities;
 using OpenQA.Selenium;
 using OpenQA.Selenium.Appium;
 using OpenQA.Selenium.Interactions;
@@ -114,6 +115,79 @@ namespace Avalonia.IntegrationTests.Appium
                 Assert.Equal(1, secondaryWindowIndex);
             }
         }
+        
+        [PlatformFact(TestPlatforms.MacOS)]
+        public void WindowOrder_Owned_Dialog_Stays_InFront_Of_FullScreen_Parent()
+        {
+            var mainWindow = _session.FindElementByAccessibilityId("MainWindow");
+
+            // Enter fullscreen
+            mainWindow.FindElementByAccessibilityId("EnterFullscreen").Click();
+            
+            // Wait for fullscreen transition.
+            Thread.Sleep(1000);
+
+            // Make sure we entered fullscreen.
+            var windowState = mainWindow.FindElementByAccessibilityId("WindowState");
+            Assert.Equal("FullScreen", windowState.Text);
+
+            // Open child window.
+            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Owned, WindowStartupLocation.Manual))
+            {
+                mainWindow.SendClick();
+                var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
+                Assert.Equal(1, secondaryWindowIndex);
+            }
+
+            // Exit fullscreen by menu shortcut Command+R
+            mainWindow.FindElementByAccessibilityId("ExitFullscreen").Click();
+
+            // Wait for restore transition.
+            Thread.Sleep(1000);
+
+            // Make sure we exited fullscreen.
+            mainWindow = _session.FindElementByAccessibilityId("MainWindow");
+            windowState = mainWindow.FindElementByAccessibilityId("WindowState");
+            Assert.Equal("Normal", windowState.Text);
+        }
+
+        [PlatformFact(TestPlatforms.MacOS)]
+        public void Does_Not_Switch_Space_From_FullScreen_To_Main_Desktop_When_FullScreen_Window_Clicked()
+        {
+            // Issue #9565
+            var mainWindow = _session.FindElementByAccessibilityId("MainWindow");
+            AppiumWebElement windowState;
+
+            // Open child window.
+            using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Owned, WindowStartupLocation.Manual))
+            {
+                // Enter fullscreen
+                mainWindow.FindElementByAccessibilityId("EnterFullscreen").Click();
+            
+                // Wait for fullscreen transition.
+                Thread.Sleep(1000);
+
+                // Make sure we entered fullscreen.
+                mainWindow = _session.FindElementByAccessibilityId("MainWindow");
+                windowState = mainWindow.FindElementByAccessibilityId("WindowState");
+                Assert.Equal("FullScreen", windowState.Text);
+                
+                // Click on main window
+                mainWindow.Click();
+
+                // Failed here due to #9565: main window is no longer visible as the main space is now shown instead
+                // of the fullscreen space.
+                mainWindow.FindElementByAccessibilityId("ExitFullscreen").Click();
+
+                // Wait for restore transition.
+                Thread.Sleep(1000);
+            }
+
+            // Make sure we exited fullscreen.
+            mainWindow = _session.FindElementByAccessibilityId("MainWindow");
+            windowState = mainWindow.FindElementByAccessibilityId("WindowState");
+            Assert.Equal("Normal", windowState.Text);
+        }
 
         [PlatformFact(TestPlatforms.MacOS)]
         public void WindowOrder_NonOwned_Window_Does_Not_Stay_InFront_Of_Parent()