Call InitializeComponent in RxUI activation tests.

To make sure activation works after loading XAML.

tests/Avalonia.ReactiveUI.UnitTests/AvaloniaActivationForViewFetcherTest.cs

@@ -10,6 +10,7 @@ using ReactiveUI;
 using DynamicData;
 using Xunit;
 using Splat;
+using Avalonia.Markup.Xaml;
 
 namespace Avalonia 
 {
@@ -70,12 +71,40 @@ namespace Avalonia
 
         public class ActivatableWindow : ReactiveWindow<ActivatableViewModel>
         {
-            public ActivatableWindow() => this.WhenActivated(disposables => { });
+            public ActivatableWindow()
+            {
+                InitializeComponent();
+                Assert.IsType<Border>(Content);
+                this.WhenActivated(disposables => { });
+            }
+
+            private void InitializeComponent()
+            {
+                var loader = new AvaloniaXamlLoader();
+                loader.Load(@"
+<Window xmlns='https://github.com/avaloniaui'>
+    <Border/>
+</Window>", null, this);
+            }
         }
 
         public class ActivatableUserControl : ReactiveUserControl<ActivatableViewModel>
         {
-            public ActivatableUserControl() => this.WhenActivated(disposables => { });
+            public ActivatableUserControl()
+            {
+                InitializeComponent();
+                Assert.IsType<Border>(Content);
+                this.WhenActivated(disposables => { });
+            }
+
+            private void InitializeComponent()
+            {
+                var loader = new AvaloniaXamlLoader();
+                loader.Load(@"
+<UserControl xmlns='https://github.com/avaloniaui'>
+    <Border/>
+</UserControl>", null, this);
+            }
         }
 
         public AvaloniaActivationForViewFetcherTest()
@@ -183,4 +212,4 @@ namespace Avalonia
             Assert.False(viewModel.IsActivated);
         }
     }
-}
+}