feat: add unit test.

tests/Test.Ursa/ImageViewerTests/Stretch_Initial_Value/StretchValueTest.cs

@@ -0,0 +1,17 @@
+using Avalonia.Controls;
+using Avalonia.Media;
+using Ursa.Controls;
+
+namespace Test.Ursa.Controls.ImageViewerTests.Stretch_Initial_Value;
+
+public class StretchValueTest
+{
+    [Fact]
+    public void Stretch_Initial_Value_Does_Not_Crash()
+    {
+        ImageViewer iv = new ImageViewer()
+        {
+            Stretch = Stretch.UniformToFill
+        };
+    }
+}