add failing test for RenderTargetBitmap_DropShadowEffect

tests/Avalonia.RenderTests/Media/RenderTargetBitmapTests.cs

@@ -0,0 +1,59 @@
+using System.Threading.Tasks;
+using Avalonia.Controls;
+using Avalonia.Controls.Shapes;
+using Avalonia.Media;
+using Avalonia.Media.Imaging;
+using Avalonia.UnitTests;
+using Xunit;
+
+namespace Avalonia.Skia.RenderTests;
+
+public class RenderTargetBitmapTests : TestBase
+{
+    public RenderTargetBitmapTests() : base(@"Media\RenderTargetBitmap")
+    {
+    }
+
+    [Fact]
+    public async Task RenderTargetBitmap_DropShadowEffect()
+    {
+        var root = new Grid
+        {
+            Width = 300,
+            Height = 300,
+            Children =
+            {
+                new Canvas
+                {
+                    Width = 300,
+                    Height = 300,
+                    Background = Brushes.White,
+                    Children =
+                    {
+                        new Rectangle
+                        {
+                            Fill = Brushes.Red,
+                            Width = 200,
+                            Height = 200,
+                            Margin = new Thickness(50),
+                            Effect = new DropShadowEffect
+                            {
+                                Color = Colors.Black,
+                                BlurRadius = 30
+                            }
+                        }
+                    }
+                }
+            }
+        };
+
+        await RenderToFile(root);
+        
+        CompareImages();
+
+        // var rtb = new RenderTargetBitmap(new PixelSize(300,300), new Vector(96,96));
+        // rtb.Render(root);
+        //
+        // rtb.Save("test.png");
+    }
+}