Add failing test for #2680.

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

@@ -1,4 +1,6 @@
 using Avalonia.Controls.Shapes;
+using Avalonia.Media;
+using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests.Shapes
@@ -12,5 +14,21 @@ namespace Avalonia.Controls.UnitTests.Shapes
 
             target.Measure(Size.Infinity);
         }
+
+        [Fact]
+        public void Subscribes_To_Geometry_Changes()
+        {
+            using var app = UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
+
+            var geometry = new EllipseGeometry { Rect = new Rect(0, 0, 10, 10) };
+            var target = new Path { Data = geometry };
+
+            target.Measure(Size.Infinity);
+            Assert.True(target.IsMeasureValid);
+
+            geometry.Rect = new Rect(0, 0, 20, 20);
+
+            Assert.False(target.IsMeasureValid);
+        }
     }
 }