feat: add headless tests.

tests/HeadlessTest.Ursa/Controls/OverlayShared/Dialog_Primary_Focus/Test.cs

@@ -0,0 +1,40 @@
+using Avalonia.Controls;
+using Avalonia.Headless.XUnit;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+using Ursa.Controls;
+
+namespace HeadlessTest.Ursa.Controls.OverlayShared.Dialog_Primary_Focus;
+
+public class Test
+{
+    [AvaloniaFact]
+    public void Normal_Dialog_Focus_On_Border()
+    {
+        var ursaWindow = new TestWindow();
+        ursaWindow.Show();
+        ursaWindow.InvokeNormalDialog();
+        Dispatcher.UIThread.RunJobs();
+        var dialog = ursaWindow.GetVisualDescendants().OfType<DefaultDialogControl>().FirstOrDefault();
+        Assert.NotNull(dialog);
+        var border = dialog.GetVisualDescendants().OfType<Border>().FirstOrDefault(a=>a.Name == "PART_Border");
+        var text = dialog.GetVisualDescendants().OfType<TextBox>().FirstOrDefault();
+        Assert.True(border?.IsFocused);
+        Assert.False(text?.IsFocused);
+    }
+    
+    [AvaloniaFact]
+    public void Focus_Dialog_Focus_On_Primary()
+    {
+        var ursaWindow = new TestWindow();
+        ursaWindow.Show();
+        ursaWindow.InvokeFocusDialog();
+        Dispatcher.UIThread.RunJobs();
+        var dialog = ursaWindow.GetVisualDescendants().OfType<DefaultDialogControl>().FirstOrDefault();
+        Assert.NotNull(dialog);
+        var border = dialog.GetVisualDescendants().OfType<Border>().FirstOrDefault(a=>a.Name == "PART_Border");
+        var text = dialog.GetVisualDescendants().OfType<TextBox>().FirstOrDefault();
+        Assert.False(border?.IsFocused);
+        Assert.True(text?.IsFocused);
+    }
+}