More tests for #4822.

Tested WPF's `Path` to confirm expected results: https://github.com/wieslawsoltes/WpfUnitTests

tests/Avalonia.Controls.UnitTests/Shapes/PathTests.cs

@@ -1,5 +1,4 @@
-using System.Runtime.InteropServices;
-using Avalonia.Controls.Shapes;
+using Avalonia.Controls.Shapes;
 using Avalonia.Media;
 using Avalonia.UnitTests;
 using Xunit;
@@ -36,6 +35,111 @@ namespace Avalonia.Controls.UnitTests.Shapes
             root.Child = null;
         }
 
+        [Theory]
+        [InlineData(Stretch.None, 100, 200)]
+        [InlineData(Stretch.Fill, 500, 500)]
+        [InlineData(Stretch.Uniform, 250, 500)]
+        [InlineData(Stretch.UniformToFill, 500, 500)]
+        public void Calculates_Correct_DesiredSize_For_Finite_Bounds(Stretch stretch, double expectedWidth, double expectedHeight)
+        {
+            using var app = UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
+
+            var target = new Path()
+            {
+                Data = new RectangleGeometry { Rect = new Rect(0, 0, 100, 200) },
+                Stretch = stretch,
+            };
+
+            target.Measure(new Size(500, 500));
+
+            Assert.Equal(new Size(expectedWidth, expectedHeight), target.DesiredSize);
+        }
+
+        [Theory]
+        [InlineData(Stretch.None)]
+        [InlineData(Stretch.Fill)]
+        [InlineData(Stretch.Uniform)]
+        [InlineData(Stretch.UniformToFill)]
+        public void Calculates_Correct_DesiredSize_For_Infinite_Bounds(Stretch stretch)
+        {
+            using var app = UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
+
+            var target = new Path()
+            {
+                Data = new RectangleGeometry { Rect = new Rect(0, 0, 100, 200) },
+                Stretch = stretch,
+            };
+
+            target.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
+
+            Assert.Equal(new Size(100, 200), target.DesiredSize);
+        }
+
+        [Fact]
+        public void Measure_Does_Not_Update_RenderedGeometry_Transform()
+        {
+            using var app = UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
+
+            var target = new Path
+            {
+                Data = new RectangleGeometry { Rect = new Rect(0, 0, 100, 200) },
+                Stretch = Stretch.Fill,
+            };
+
+            target.Measure(new Size(500, 500));
+
+            Assert.Null(target.RenderedGeometry.Transform);
+        }
+
+        [Theory]
+        [InlineData(Stretch.None, 1, 1)]
+        [InlineData(Stretch.Fill, 5, 2.5)]
+        [InlineData(Stretch.Uniform, 2.5, 2.5)]
+        [InlineData(Stretch.UniformToFill, 5, 5)]
+        public void Arrange_Updates_RenderedGeometry_Transform(Stretch stretch, double expectedScaleX, double expectedScaleY)
+        {
+            using var app = UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
+
+            var target = new Path
+            {
+                Data = new RectangleGeometry { Rect = new Rect(0, 0, 100, 200) },
+                Stretch = stretch,
+            };
+
+            target.Measure(new Size(500, 500));
+            target.Arrange(new Rect(0, 0, 500, 500));
+
+            if (expectedScaleX == 1 && expectedScaleY == 1)
+            {
+                Assert.Null(target.RenderedGeometry.Transform);
+            }
+            else
+            {
+                Assert.Equal(Matrix.CreateScale(expectedScaleX, expectedScaleY), target.RenderedGeometry.Transform.Value);
+            }
+        }
+
+        [Fact]
+        public void Measure_Without_Arrange_Does_Not_Clear_RenderedGeometry_Transform()
+        {
+            using var app = UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
+
+            var target = new Path
+            {
+                Data = new RectangleGeometry { Rect = new Rect(0, 0, 100, 100) },
+                Stretch = Stretch.Fill,
+            };
+
+            target.Measure(new Size(200, 200));
+            target.Arrange(new Rect(0, 0, 200, 200));
+
+            Assert.Equal(Matrix.CreateScale(2, 2), target.RenderedGeometry.Transform.Value);
+
+            target.Measure(new Size(300, 300));
+
+            Assert.Equal(Matrix.CreateScale(2, 2), target.RenderedGeometry.Transform.Value);
+        }
+
         [Fact]
         public void Arrange_Without_Measure_Updates_RenderedGeometry_Transform()
         {