Added unit tests

tests/Avalonia.RenderTests/Avalonia.RenderTests.projitems

@@ -14,6 +14,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Media\RadialGradientBrushTests.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Media\BitmapTests.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)OpacityMaskTests.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Shapes\ShapeTests.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)SVGPathTests.cs" />
     <Compile Include="Media\FormattedTextImplTests.cs" />
     <Compile Include="Controls\ImageTests.cs" />

tests/Avalonia.RenderTests/Shapes/ShapeTests.cs

@@ -0,0 +1,112 @@
+using System.Collections.Generic;
+using Avalonia.Controls;
+using Avalonia.Controls.Shapes;
+using Avalonia.Media;
+using Xunit;
+
+
+#if AVALONIA_SKIA
+namespace Avalonia.Skia.RenderTests
+#else
+namespace Avalonia.Direct2D1.RenderTests.Shapes
+#endif
+{
+    public class ShapeTests : TestBase
+    {
+        public ShapeTests()
+            : base(@"Shapes\Shape")
+        { }
+
+        [Fact]
+        public void Shape_Transformation_Calculation_Should_Be_Deferred_To_Arrange_When_Strech_Is_Fill_And_Aviable_Size_Is_Infinite()
+        {
+            var shape = new Polygon()
+            {
+                Points = new List<Point>
+                {
+                    new Point(0, 0),
+                    new Point(10, 5),
+                    new Point(0, 10)
+                },
+                Stretch = Stretch.Fill
+            };
+
+            var availableSize = new Size(double.PositiveInfinity, double.PositiveInfinity);
+            shape.Measure(availableSize);
+            Geometry postMeasureGeometry = shape.RenderedGeometry;
+            Transform postMeasureTransform = postMeasureGeometry.Transform;
+
+            var finalSize = new Size(100, 50);
+            var finalRect = new Rect(finalSize);
+            shape.Arrange(finalRect);
+
+            Geometry postArrangeGeometry = shape.RenderedGeometry;
+            Transform postArrangeTransform = postArrangeGeometry.Transform;
+
+            Assert.NotEqual(postMeasureGeometry, postArrangeGeometry);
+            Assert.NotEqual(postMeasureTransform, postArrangeTransform);
+            Assert.Equal(finalSize, shape.Bounds.Size);
+        }
+
+        [Fact]
+        public void Shape_Transformation_Calculation_Should_Not_Be_Deferred_To_Arrange_When_Strech_Is_Fill_And_Aviable_Size_Is_Finite()
+        {
+            var shape = new Polygon()
+            {
+                Points = new List<Point>
+                {
+                    new Point(0, 0),
+                    new Point(10, 5),
+                    new Point(0, 10)
+                },
+                Stretch = Stretch.Fill
+            };
+
+            var availableSize = new Size(100, 50);
+            shape.Measure(availableSize);
+            Geometry postMeasureGeometry = shape.RenderedGeometry;
+            Transform postMeasureTransform = postMeasureGeometry.Transform;
+
+            var finalRect = new Rect(availableSize);
+            shape.Arrange(finalRect);
+
+            Geometry postArrangeGeometry = shape.RenderedGeometry;
+            Transform postArrangeTransform = postArrangeGeometry.Transform;
+
+            Assert.Equal(postMeasureGeometry, postArrangeGeometry);
+            Assert.Equal(postMeasureTransform, postArrangeTransform);
+            Assert.Equal(availableSize, shape.Bounds.Size);
+        }
+
+        [Fact]
+        public void Shape_Transformation_Calculation_Should_Not_Be_Deferred_To_Arrange_When_Strech_Is_None()
+        {
+            var shape = new Polygon()
+            {
+                Points = new List<Point>
+                {
+                    new Point(0, 0),
+                    new Point(10, 5),
+                    new Point(0, 10)
+                },
+                Stretch = Stretch.None
+            };
+
+            var availableSize = new Size(double.PositiveInfinity, double.PositiveInfinity);
+            shape.Measure(availableSize);
+            Geometry postMeasureGeometry = shape.RenderedGeometry;
+            Transform postMeasureTransform = postMeasureGeometry.Transform;
+
+            var finalSize = new Size(100, 50);
+            var finalRect = new Rect(finalSize);
+            shape.Arrange(finalRect);
+
+            Geometry postArrangeGeometry = shape.RenderedGeometry;
+            Transform postArrangeTransform = postArrangeGeometry.Transform;
+
+            Assert.Equal(postMeasureGeometry, postArrangeGeometry);
+            Assert.Equal(postMeasureTransform, postArrangeTransform);
+            Assert.Equal(finalSize, shape.Bounds.Size);
+        }
+    }
+}