feat: add tests.

tests/HeadlessTest.Ursa/Controls/PanelTests/WrapPanelWithTrailingItemTests.cs

@@ -0,0 +1,155 @@
+using Avalonia.Controls;
+using Avalonia.Headless.XUnit;
+using Avalonia.Layout;
+using Avalonia.LogicalTree;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+using Ursa.Controls.Panels;
+
+namespace HeadlessTest.Ursa.Controls.PanelTests;
+
+public class WrapPanelWithTrailingItemTests
+{
+    [Fact]
+    public void Visual_Children_Correct()
+    {
+        var panel = new WrapPanelWithTrailingItem();
+        var child1 = new Button { Content = "Button 1"};
+        var child2 = new Button { Content = "Button 2"};
+        var trailing = new Button { Content = "Trailing"};
+        
+        panel.Children.Add(child1);
+        panel.Children.Add(child2);
+        panel.TrailingItem = trailing;
+        
+        var visualChildren = panel.GetVisualChildren().ToList();
+        Assert.Equal(3, visualChildren.Count);
+        Assert.Equal(child1, visualChildren[0]);
+        Assert.Equal(child2, visualChildren[1]);
+        Assert.Equal(trailing, visualChildren[2]);
+        
+        var child3 = new Button { Content = "Button 3"};
+        panel.Children.Add(child3);
+        
+        visualChildren = panel.GetVisualChildren().ToList();
+        Assert.Equal(4, visualChildren.Count);
+        Assert.Equal(child1, visualChildren[0]);
+        Assert.Equal(child2, visualChildren[1]);
+        Assert.Equal(child3, visualChildren[2]);
+        Assert.Equal(trailing, visualChildren[3]);
+        
+        var trailing2 = new Button { Content = "Trailing2"};
+        panel.TrailingItem = trailing2;
+        
+        visualChildren = panel.GetVisualChildren().ToList();
+        Assert.Equal(4, visualChildren.Count);
+        Assert.Equal(child1, visualChildren[0]);
+        Assert.Equal(child2, visualChildren[1]);
+        Assert.Equal(child3, visualChildren[2]);
+        Assert.Equal(trailing2, visualChildren[3]);
+
+        panel.Children.Remove(child2);
+        
+        visualChildren = panel.GetVisualChildren().ToList();
+        Assert.Equal(3, visualChildren.Count);
+        Assert.Equal(child1, visualChildren[0]);
+        Assert.Equal(child3, visualChildren[1]);
+        Assert.Equal(trailing2, visualChildren[2]);
+    }
+    
+    [Fact]
+    // Items Appears in Logical Children because IsItemsHost is false for individual Panels
+    public void Logical_Children_Correct()
+    {
+        var panel = new WrapPanelWithTrailingItem();
+        var child1 = new Button { Content = "Button 1"};
+        var child2 = new Button { Content = "Button 2"};
+        var trailing = new Button { Content = "Trailing"};
+        
+        panel.Children.Add(child1);
+        panel.Children.Add(child2);
+        panel.TrailingItem = trailing;
+        
+        var logicalChildren = panel.GetLogicalChildren().ToList();
+        Assert.Equal(3, logicalChildren.Count);
+        Assert.Equal(child1, logicalChildren[0]);
+        Assert.Equal(child2, logicalChildren[1]);
+        Assert.Equal(trailing, logicalChildren[2]);
+        
+        var child3 = new Button { Content = "Button 3"};
+        panel.Children.Add(child3);
+        
+        logicalChildren = panel.GetLogicalChildren().ToList();
+        Assert.Equal(4, logicalChildren.Count);
+        Assert.Equal(child1, logicalChildren[0]);
+        Assert.Equal(child2, logicalChildren[1]);
+        Assert.Equal(child3, logicalChildren[2]);
+        Assert.Equal(trailing, logicalChildren[3]);
+        
+        var trailing2 = new Button { Content = "Trailing2"};
+        panel.TrailingItem = trailing2;
+        
+        logicalChildren = panel.GetLogicalChildren().ToList();
+        Assert.Equal(4, logicalChildren.Count);
+        Assert.Equal(child1, logicalChildren[0]);
+        Assert.Equal(child2, logicalChildren[1]);
+        Assert.Equal(child3, logicalChildren[2]);
+        Assert.Equal(trailing2, logicalChildren[3]);
+
+        panel.Children.Remove(child2);
+        
+        logicalChildren = panel.GetLogicalChildren().ToList();
+        Assert.Equal(3, logicalChildren.Count);
+        Assert.Equal(child1, logicalChildren[0]);
+        Assert.Equal(child3, logicalChildren[1]);
+        Assert.Equal(trailing2, logicalChildren[2]);
+    }
+
+    [AvaloniaFact]
+    public void Measure_Arrange_Children()
+    {
+        var window = new Window()
+        {
+            Height = 1000, Width = 1000, VerticalContentAlignment = VerticalAlignment.Stretch
+        };
+        var panel = new WrapPanelWithTrailingItem();
+        var child1 = new Button { Content = "Button 1", Width = 200, Height = 100 };
+        var child2 = new Button { Content = "Button 2", Width = 300, Height = 100 };
+        var trailing = new Button
+        {
+            Content = "Trailing", 
+            Height = 100, 
+            HorizontalAlignment = HorizontalAlignment.Stretch
+        };
+        window.Content = panel;
+        panel.Children.Add(child1);
+        panel.Children.Add(child2);
+        panel.TrailingItem = trailing;
+        
+        window.Show();
+        Dispatcher.UIThread.RunJobs();
+        Assert.Equal(200, child1.Bounds.Width);
+        Assert.Equal(300, child2.Bounds.Width);
+        Assert.Equal(500, trailing.Bounds.Width);
+        
+        panel.Width = 600;
+        Dispatcher.UIThread.RunJobs();
+        Assert.Equal(200, child1.Bounds.Width);
+        Assert.Equal(300, child2.Bounds.Width);
+        Assert.Equal(100, trailing.Bounds.Width);
+
+        panel.Width = 510;
+        Dispatcher.UIThread.RunJobs();
+        Assert.Equal(200, child1.Bounds.Width);
+        Assert.Equal(300, child2.Bounds.Width);
+        Assert.Equal(510, trailing.Bounds.Width);
+        Assert.Equal(100, trailing.Bounds.Y);
+        
+        panel.Width = 300;
+        Dispatcher.UIThread.RunJobs();
+        Assert.Equal(200, child1.Bounds.Width);
+        Assert.Equal(300, child2.Bounds.Width);
+        Assert.Equal(300, trailing.Bounds.Width);
+        Assert.Equal(200, trailing.Bounds.Y);
+    }
+}