add tests for reflection binding for casting in path

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs

@@ -84,6 +84,54 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
             }
         }
 
+        [Fact]
+        public void SupportCastToTypeInExpression()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'
+        >
+    <ContentControl Content='{Binding $parent.DataContext(local:TestDataContext).StringProperty}' Name='contentControl' />
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var contentControl = window.FindControl<ContentControl>("contentControl");
+
+                var dataContext = new TestDataContext
+                {
+                    StringProperty = "foobar"
+                };
+
+                window.DataContext = dataContext;
+
+                Assert.Equal(dataContext.StringProperty, contentControl.Content);
+            }
+        }
+
+        [Fact]
+        public void SupportCastToTypeInExpression_DifferentTypeEvaluatesToNull()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'
+        >
+    <ContentControl Content='{Binding $parent.DataContext(local:TestDataContext)}' Name='contentControl' />
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var contentControl = window.FindControl<ContentControl>("contentControl");
+
+                var dataContext = "foo";
+
+                window.DataContext = dataContext;
+
+                Assert.Equal(null, contentControl.Content);
+            }
+        }
         private class FooBar
         {
             public object Foo { get; } = null;