Added failing test for #4900.

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

@@ -0,0 +1,24 @@
+using Avalonia.Controls;
+using Avalonia.Media;
+using Xunit;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Xaml
+{
+    public class ShapeTests : XamlTestBase
+    {
+        [Fact]
+        public void Can_Specify_DashStyle_In_XAML()
+        {
+            var xaml = @"
+<Pen xmlns='https://github.com/avaloniaui'>
+    <Pen.DashStyle>
+	    <DashStyle Offset='0' Dashes='1,3'/>
+    </Pen.DashStyle>
+</Pen>";
+
+            var target = AvaloniaRuntimeXamlLoader.Parse<Pen>(xaml);
+
+            Assert.NotNull(target);
+        }
+    }
+}