Added failing tests for #2470.

tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs

@@ -100,6 +100,28 @@ namespace Avalonia.Markup.UnitTests.Data
             Assert.Equal("baz", target.Text);
         }
 
+        [Fact]
+        public void OneWayToSource_Binding_Should_React_To_DataContext_Changed()
+        {
+            var target = new TextBlock { Text = "bar" };
+            var binding = new Binding
+            {
+                Path = "Foo",
+                Mode = BindingMode.OneWayToSource,
+            };
+
+            target.Bind(TextBox.TextProperty, binding);
+
+            var source = new Source { Foo = "foo" };
+            target.DataContext = source;
+
+            Assert.Equal("bar", source.Foo);
+            target.Text = "baz";
+            Assert.Equal("baz", source.Foo);
+            source.Foo = "quz";
+            Assert.Equal("baz", target.Text);
+        }
+
         [Fact]
         public void Default_BindingMode_Should_Be_Used()
         {

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests.cs

@@ -329,6 +329,33 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 
                 Assert.Equal("Hello world", textBlock.Text); 
             }
-        } 
+        }
+
+        [Fact]
+        public void Binding_OneWayToSource_Works()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        ShowInTaskbar='{Binding ShowInTaskbar, Mode=OneWayToSource}'>
+</Window>";
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var viewModel = new WindowViewModel();
+
+                window.DataContext = viewModel;
+                window.ApplyTemplate();
+
+                Assert.True(window.ShowInTaskbar);
+                Assert.True(viewModel.ShowInTaskbar);
+            }
+        }
+
+        private class WindowViewModel
+        {
+            public bool ShowInTaskbar { get; set; }
+        }
     }
 }