feat: add unit test. fix various issues discovered in test.

tests/HeadlessTest.Ursa/Semi/LocalizationTest.cs

@@ -0,0 +1,101 @@
+using System.Globalization;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Headless.XUnit;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+using Semi.Avalonia.Locale;
+using Ursa.Controls;
+using Ursa.Themes.Semi;
+
+namespace HeadlessTest.Ursa.Semi;
+
+public class LocalizationTest
+{
+    [AvaloniaFact]
+    public void Default_Locale_Is_Chinese()
+    {
+        var window = new UrsaWindow();
+        window.Show();
+        MessageBox.ShowOverlayAsync("Hello World", button: MessageBoxButton.YesNo, toplevelHashCode: window.GetHashCode());
+        Task.Delay(100).Wait();
+        Dispatcher.UIThread.RunJobs();
+        var dialog = window.GetVisualDescendants().OfType<MessageBoxControl>().SingleOrDefault();
+        var yesButton = dialog?.GetVisualDescendants().OfType<Button>().FirstOrDefault(b => b.Name == "PART_YesButton");
+        Assert.Equal("是", yesButton?.Content?.ToString());
+    }
+    
+    [AvaloniaFact]
+    public void Set_English_Works()
+    {
+        var window = new UrsaWindow();
+        window.Show();
+        MessageBox.ShowOverlayAsync("Hello World", button: MessageBoxButton.YesNo, toplevelHashCode: window.GetHashCode());
+        Task.Delay(100).Wait();
+        Dispatcher.UIThread.RunJobs();
+        var dialog = window.GetVisualDescendants().OfType<MessageBoxControl>().SingleOrDefault();
+        var yesButton = dialog?.GetVisualDescendants().OfType<Button>().FirstOrDefault(b => b.Name == "PART_YesButton");
+        Assert.Equal("是", yesButton?.Content?.ToString());
+        Assert.NotNull(Application.Current);
+        SemiTheme.OverrideLocaleResources(Application.Current, new CultureInfo("en-US"));
+        Assert.Equal("Yes", yesButton?.Content?.ToString());
+    }
+    
+    [AvaloniaFact]
+    public void Set_NonExisting_Culture_Does_Nothing()
+    {
+        var window = new UrsaWindow();
+        window.Show();
+        MessageBox.ShowOverlayAsync("Hello World", button: MessageBoxButton.YesNo, toplevelHashCode: window.GetHashCode());
+        Task.Delay(100).Wait();
+        Dispatcher.UIThread.RunJobs();
+        var dialog = window.GetVisualDescendants().OfType<MessageBoxControl>().SingleOrDefault();
+        var yesButton = dialog?.GetVisualDescendants().OfType<Button>().FirstOrDefault(b => b.Name == "PART_YesButton");
+        Assert.Equal("是", yesButton?.Content?.ToString());
+        Assert.NotNull(Application.Current);
+        // We expect there won't be anyone adding Armenian localization... Subject to change.
+        SemiTheme.OverrideLocaleResources(Application.Current, new CultureInfo("hy-AM"));
+        Assert.Equal("是", yesButton?.Content?.ToString());
+        SemiTheme.OverrideLocaleResources(Application.Current, null);
+        Assert.Equal("是", yesButton?.Content?.ToString());
+    }
+    
+    [AvaloniaFact]
+    public void Set_English_To_Control_Works()
+    {
+        var window = new UrsaWindow();
+        window.Show();
+        MessageBox.ShowOverlayAsync("Hello World", button: MessageBoxButton.YesNo, toplevelHashCode: window.GetHashCode());
+        Task.Delay(100).Wait();
+        Dispatcher.UIThread.RunJobs();
+        var dialog = window.GetVisualDescendants().OfType<MessageBoxControl>().SingleOrDefault();
+        var yesButton = dialog?.GetVisualDescendants().OfType<Button>().FirstOrDefault(b => b.Name == "PART_YesButton");
+        Assert.Equal("是", yesButton?.Content?.ToString());
+        Assert.NotNull(Application.Current);
+        SemiTheme.OverrideLocaleResources(window, new CultureInfo("en-US"));
+        Assert.Equal("Yes", yesButton?.Content?.ToString());
+    }
+    
+    [Fact]
+    public void SemiTheme_Localization_Behavior()
+    {
+        var theme = new SemiTheme();
+        Assert.Null(theme.Locale);
+        theme.Locale = new CultureInfo("en-US");
+        Assert.Equal(new CultureInfo("en-US"), theme.Locale);
+        var yesText = theme.Resources["STRING_MENU_DIALOG_YES"];
+        Assert.Equal("Yes", yesText);
+        theme.Locale = new CultureInfo("zh-CN");
+        Assert.Equal(new CultureInfo("zh-CN"), theme.Locale);
+        yesText = theme.Resources["STRING_MENU_DIALOG_YES"];
+        Assert.Equal("是", yesText);
+        theme.Locale = new CultureInfo("hy-AM");
+        Assert.Equal(new CultureInfo("zh-CN"), theme.Locale);
+        yesText = theme.Resources["STRING_MENU_DIALOG_YES"];
+        Assert.Equal("是", yesText);
+        theme.Locale = null;
+        Assert.Equal(new CultureInfo("zh-CN"), theme.Locale);
+        yesText = theme.Resources["STRING_MENU_DIALOG_YES"];
+        Assert.Equal("是", yesText);
+    }
+}