Fix even more tests.

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/DynamicResourceExtensionTests.cs

@@ -33,7 +33,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
             DelayedBinding.ApplyBindings(border);
 
-            var brush = (SolidColorBrush)border.Background;
+            var brush = (ISolidColorBrush)border.Background;
             Assert.Equal(0xff506070, brush.Color.ToUint32());
         }
 
@@ -80,7 +80,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
             DelayedBinding.ApplyBindings(border);
 
-            var brush = (SolidColorBrush)border.Background;
+            var brush = (ISolidColorBrush)border.Background;
             Assert.Equal(0xff506070, brush.Color.ToUint32());
         }
 
@@ -108,7 +108,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
             DelayedBinding.ApplyBindings(border);
 
-            var brush = (SolidColorBrush)border.Background;
+            var brush = (ISolidColorBrush)border.Background;
             Assert.Equal(0xff506070, brush.Color.ToUint32());
         }
 
@@ -140,7 +140,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
             DelayedBinding.ApplyBindings(border);
 
-            var brush = (SolidColorBrush)border.Background;
+            var brush = (ISolidColorBrush)border.Background;
             Assert.Equal(0xff506070, brush.Color.ToUint32());
         }
 
@@ -212,7 +212,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
                 var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
                 var button = window.FindControl<Button>("button");
-                var brush = (SolidColorBrush)button.Background;
+                var brush = (ISolidColorBrush)button.Background;
 
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
             }
@@ -241,7 +241,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
                 var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
                 var button = window.FindControl<Button>("button");
-                var brush = (SolidColorBrush)button.Background;
+                var brush = (ISolidColorBrush)button.Background;
 
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
             }
@@ -275,7 +275,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
                 var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
                 var border = window.FindControl<Border>("border");
-                var brush = (SolidColorBrush)border.Background;
+                var brush = (ISolidColorBrush)border.Background;
 
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
             }
@@ -317,7 +317,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
                 window.Show();
 
                 var border = (Border)button.GetVisualChildren().Single();
-                var brush = (SolidColorBrush)border.Background;
+                var brush = (ISolidColorBrush)border.Background;
 
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
             }
@@ -648,7 +648,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
                 DelayedBinding.ApplyBindings(border);
 
-                var brush = (SolidColorBrush)border.Background;
+                var brush = (ISolidColorBrush)border.Background;
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
 
                 window.Content = null;
@@ -657,7 +657,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
                 window.Content = border;
 
-                brush = (SolidColorBrush)border.Background;
+                brush = (ISolidColorBrush)border.Background;
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
             }
         }

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/ResourceIncludeTests.cs

@@ -39,7 +39,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
                     var userControl = (UserControl)AvaloniaRuntimeXamlLoader.Load(xaml);
                     var border = userControl.FindControl<Border>("border");
 
-                    var brush = (SolidColorBrush)border.Background;
+                    var brush = (ISolidColorBrush)border.Background;
                     Assert.Equal(0xff506070, brush.Color.ToUint32());
                 }
             }

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BasicTests.cs

@@ -512,7 +512,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             style.TryGetResource("Brush", out var brush);
 
             Assert.NotNull(brush);
-            Assert.IsType<SolidColorBrush>(brush);
+            Assert.IsAssignableFrom<ISolidColorBrush>(brush);
             Assert.Equal(Colors.White, ((ISolidColorBrush)brush).Color);
 
             style.TryGetResource("Double", out var d);

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/StyleTests.cs

@@ -101,7 +101,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
     </UserControl.Styles>
 </UserControl>";
                 var userControl = (UserControl)AvaloniaRuntimeXamlLoader.Load(xaml);
-                var brush = (SolidColorBrush)((Style)userControl.Styles[0]).Resources["brush"];
+                var brush = (ISolidColorBrush)((Style)userControl.Styles[0]).Resources["brush"];
 
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
             }