Add failing tests for #2838.

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

@@ -278,5 +278,67 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
                 Assert.Equal(Colors.Red, ((ISolidColorBrush)notFoo.Background).Color);
             }
         }
+
+        [Fact]
+        public void Style_Can_Use_Or_Selector_1()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+             xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Window.Styles>
+        <Style Selector='Border.foo, Border.bar'>
+            <Setter Property='Background' Value='Red'/>
+        </Style>
+    </Window.Styles>
+    <StackPanel>
+        <Border Name='foo' Classes='foo'/>
+        <Border Name='bar' Classes='bar'/>
+        <Border Name='baz' Classes='baz'/>
+    </StackPanel>
+</Window>";
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var foo = window.FindControl<Border>("foo");
+                var bar = window.FindControl<Border>("bar");
+                var baz = window.FindControl<Border>("baz");
+
+                Assert.Equal(Brushes.Red, foo.Background);
+                Assert.Equal(Brushes.Red, bar.Background);
+                Assert.Null(baz.Background);
+            }
+        }
+
+        [Fact]
+        public void Style_Can_Use_Or_Selector_2()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+             xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Window.Styles>
+        <Style Selector='Border,Canvas,ListBox'>
+            <Setter Property='Background' Value='Red'/>
+        </Style>
+    </Window.Styles>
+    <StackPanel>
+        <Border Name='border'/>
+        <Canvas Name='canvas'/>
+        <ListBox Name='listBox'/>
+    </StackPanel>
+</Window>";
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var border = window.FindControl<Border>("border");
+                var canvas = window.FindControl<Canvas>("canvas");
+                var listBox = window.FindControl<ListBox>("listBox");
+
+                Assert.Equal(Brushes.Red, border.Background);
+                Assert.Equal(Brushes.Red, canvas.Background);
+                Assert.Equal(Brushes.Red, listBox.Background);
+            }
+        }
     }
 }