Added failing render test.

Deferred rendering does not yet support clipping in `Visual.Render`.

tests/Avalonia.RenderTests/Controls/CustomRenderTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Layout;
@@ -23,37 +24,68 @@ namespace Avalonia.Direct2D1.RenderTests.Controls
         }
 
         [Fact]
-        public async Task Opacity()
+        public async Task Clip()
         {
             Decorator target = new Decorator
             {
                 Padding = new Thickness(8),
                 Width = 200,
                 Height = 200,
-                Child = new OpacityRenderer(),
+                Child = new CustomRenderer((control, context) =>
+                {
+                    context.FillRectangle(
+                        Brushes.Red,
+                        control.Bounds,
+                        4);
+
+                    using (context.PushClip(control.Bounds.Deflate(20)))
+                    {
+                        context.FillRectangle(
+                            Brushes.Blue,
+                            control.Bounds,
+                            4);
+                    }
+                }),
             };
 
             await RenderToFile(target);
             CompareImages();
         }
 
-        class OpacityRenderer : Control
+        [Fact]
+        public async Task Opacity()
         {
-            public override void Render(DrawingContext context)
+            Decorator target = new Decorator
             {
-                context.FillRectangle(
-                    Brushes.Red,
-                    Bounds,
-                    4);
-
-                using (context.PushOpacity(0.5))
+                Padding = new Thickness(8),
+                Width = 200,
+                Height = 200,
+                Child = new CustomRenderer((control, context) =>
                 {
                     context.FillRectangle(
-                        Brushes.Blue,
-                        Bounds.Deflate(20),
+                        Brushes.Red,
+                        control.Bounds,
                         4);
-                }
-            }
+
+                    using (context.PushOpacity(0.5))
+                    {
+                        context.FillRectangle(
+                            Brushes.Blue,
+                            control.Bounds.Deflate(20),
+                            4);
+                    }
+                }),
+            };
+
+            await RenderToFile(target);
+            CompareImages();
+        }
+
+        class CustomRenderer : Control
+        {
+            private Action<CustomRenderer, DrawingContext> _render;
+            public CustomRenderer(Action<CustomRenderer, DrawingContext> render) => _render = render;
+            public override void Render(DrawingContext context) => _render(this, context);
         }
     }
 }