diff --git a/tests/Perspex.SceneGraph.UnitTests/RelativeRectComparer.cs b/tests/Perspex.SceneGraph.UnitTests/RelativeRectComparer.cs
new file mode 100644
index 0000000000..cbde00e36c
--- /dev/null
+++ b/tests/Perspex.SceneGraph.UnitTests/RelativeRectComparer.cs
@@ -0,0 +1,25 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+
+namespace Perspex.SceneGraph.UnitTests
+{
+    public class RelativeRectComparer : IEqualityComparer<RelativeRect>
+    {
+        public bool Equals(RelativeRect a, RelativeRect b)
+        {
+            return a.Unit == b.Unit &&
+                   Math.Round(a.Rect.X, 3) == Math.Round(b.Rect.X, 3) &&
+                   Math.Round(a.Rect.Y, 3) == Math.Round(b.Rect.Y, 3) &&
+                   Math.Round(a.Rect.Width, 3) == Math.Round(b.Rect.Width, 3) &&
+                   Math.Round(a.Rect.Height, 3) == Math.Round(b.Rect.Height, 3);
+        }
+
+        public int GetHashCode(Rect obj)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}