Add comprehensive headless tests for 10 controls with enhanced ItemsSource and method testing (#18)

* Initial plan

* Add comprehensive tests for 5 controls: Avatar, Clock, ClockTicks, AspectRatioLayout, AspectRatioLayoutItem

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* Complete comprehensive headless tests for all 10 controls - added 72 more tests

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* Add requested test cases for MultiComboBox and TreeComboBox - ItemsSource, Remove, Clear, hierarchical data

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* test: open dropdown to trigger materialization.

* test: set CurrentCulture to en-US for calendar view tests

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>
Co-authored-by: rabbitism <dongbin@irihi.tech>

tests/HeadlessTest.Ursa/Controls/TreeComboBoxItemTests/TreeComboBoxItemTests.cs

@@ -0,0 +1,258 @@
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Headless.XUnit;
+using UrsaControls = Ursa.Controls;
+
+namespace HeadlessTest.Ursa.Controls.TreeComboBoxItemTests;
+
+public class TreeComboBoxItemTests
+{
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Initialize_With_Default_Values()
+    {
+        // Arrange & Act
+        var item = new UrsaControls.TreeComboBoxItem();
+
+        // Assert
+        Assert.False(item.IsSelected);
+        Assert.False(item.IsExpanded);
+        Assert.True(item.IsSelectable);
+        Assert.Equal(0, item.Level);
+        Assert.Null(item.Header);
+        Assert.Null(item.Owner);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Set_IsSelected_Property()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.IsSelected = true;
+
+        // Assert
+        Assert.True(item.IsSelected);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Set_IsExpanded_Property()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.IsExpanded = true;
+
+        // Assert
+        Assert.True(item.IsExpanded);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Set_IsSelectable_Property()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.IsSelectable = false;
+
+        // Assert
+        Assert.False(item.IsSelectable);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Set_Header_Property()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        var header = "Test Header";
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.Header = header;
+
+        // Assert
+        Assert.Equal(header, item.Header);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Set_Header_As_Control()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        var header = new Button { Content = "Header Button" };
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.Header = header;
+
+        // Assert
+        Assert.Equal(header, item.Header);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Add_Child_Items()
+    {
+        // Arrange
+        var window = new Window();
+        var parentItem = new UrsaControls.TreeComboBoxItem { Header = "Parent" };
+        var childItem1 = new UrsaControls.TreeComboBoxItem { Header = "Child 1" };
+        var childItem2 = new UrsaControls.TreeComboBoxItem { Header = "Child 2" };
+        window.Content = parentItem;
+        window.Show();
+
+        // Act
+        parentItem.Items.Add(childItem1);
+        parentItem.Items.Add(childItem2);
+
+        // Assert
+        Assert.Equal(2, parentItem.Items.Count);
+        Assert.Equal(2, parentItem.ItemCount);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Be_Visible_When_Added_To_Window()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+
+        // Act
+        window.Content = item;
+        window.Show();
+
+        // Assert
+        Assert.True(item.IsVisible);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Inherit_From_ItemsControl()
+    {
+        // Arrange & Act
+        var item = new UrsaControls.TreeComboBoxItem();
+
+        // Assert
+        Assert.IsAssignableFrom<ItemsControl>(item);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Toggle_Selection()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.IsSelected = true;
+        item.IsSelected = false;
+
+        // Assert
+        Assert.False(item.IsSelected);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Toggle_Expansion()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.IsExpanded = true;
+        item.IsExpanded = false;
+
+        // Assert
+        Assert.False(item.IsExpanded);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Handle_Null_Header()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.Header = "Test";
+        item.Header = null;
+
+        // Assert
+        Assert.Null(item.Header);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Support_DataContext()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        var dataContext = new { Name = "Test", IsEnabled = true };
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.DataContext = dataContext;
+
+        // Assert
+        Assert.Equal(dataContext, item.DataContext);
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Handle_Selection_When_Not_Selectable()
+    {
+        // Arrange
+        var window = new Window();
+        var item = new UrsaControls.TreeComboBoxItem();
+        window.Content = item;
+        window.Show();
+
+        // Act
+        item.IsSelectable = false;
+        item.IsSelected = true; // Should still work programmatically
+
+        // Assert
+        Assert.False(item.IsSelectable);
+        Assert.True(item.IsSelected); // Still can be selected programmatically
+    }
+
+    [AvaloniaFact]
+    public void TreeComboBoxItem_Should_Handle_Nested_Items()
+    {
+        // Arrange
+        var window = new Window();
+        var rootItem = new UrsaControls.TreeComboBoxItem { Header = "Root" };
+        var childItem = new UrsaControls.TreeComboBoxItem { Header = "Child" };
+        var grandChildItem = new UrsaControls.TreeComboBoxItem { Header = "GrandChild" };
+        window.Content = rootItem;
+        window.Show();
+
+        // Act
+        childItem.Items.Add(grandChildItem);
+        rootItem.Items.Add(childItem);
+
+        // Assert
+        Assert.Single(rootItem.Items);
+        Assert.Single(childItem.Items);
+        Assert.Empty(grandChildItem.Items);
+    }
+}