add failing tests for parsing points in xaml

tests/Avalonia.Markup.Xaml.UnitTests/Converters/PointsListTypeConverterTests.cs

@@ -0,0 +1,28 @@
+using System.Collections.Generic;
+using Avalonia.Controls.Shapes;
+using Avalonia.Markup.Xaml.Converters;
+using Xunit;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Converters
+{
+    public class PointsListTypeConverterTests
+    {
+        [Theory]
+        [InlineData("1,2 3,4")]
+        [InlineData("1 2 3 4")]
+        [InlineData("1 2,3 4")]
+        [InlineData("1,2,3,4")]
+        public void Should_Parse_Points_in_Xaml(string input)
+        {
+            var xaml = $"<Polygon xmlns='https://github.com/avaloniaui' Points='{input}' />";
+            var loader = new AvaloniaXamlLoader();
+            var polygon = (Polygon)loader.Load(xaml);
+
+            var points = polygon.Points;
+
+            Assert.Equal(2, points.Count);
+            Assert.Equal(new Point(1, 2), points[0]);
+            Assert.Equal(new Point(3, 4), points[1]);
+        }
+    }
+}