Add failing unit test for #10420.

tests/Avalonia.Controls.UnitTests/Primitives/PopupTests.cs

@@ -18,6 +18,7 @@ using Avalonia.Input;
 using Avalonia.Rendering;
 using System.Threading.Tasks;
 using Avalonia.Threading;
+using Avalonia.Interactivity;
 
 namespace Avalonia.Controls.UnitTests.Primitives
 {
@@ -1048,6 +1049,30 @@ namespace Avalonia.Controls.UnitTests.Primitives
             }            
         }
 
+        [Fact]
+        public void Events_Should_Be_Routed_To_Popup_Parent()
+        {
+            using (CreateServices())
+            {
+                var popupContent = new Border();
+                var popup = new Popup { Child = popupContent };
+                var popupParent = new Border { Child = popup };
+                var root = PreparedWindow(popupParent);
+                var raised = 0;
+
+                root.LayoutManager.ExecuteInitialLayoutPass();
+                popup.Open();
+                root.LayoutManager.ExecuteLayoutPass();
+
+                var ev = new RoutedEventArgs(Button.ClickEvent);
+
+                popupParent.AddHandler(Button.ClickEvent, (s, e) => ++raised);
+                popupContent.RaiseEvent(ev);
+
+                Assert.Equal(1, raised);
+            }
+        }
+
         private IDisposable CreateServices()
         {
             return UnitTestApplication.Start(TestServices.StyledWindow.With(windowingPlatform: