feat: rename AnchorId to Id and add TopOffset property. Add headless tests.

tests/HeadlessTest.Ursa/Controls/AnchorTests/Tests.cs

@@ -0,0 +1,82 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Headless;
+using Avalonia.Headless.XUnit;
+using Avalonia.Input;
+using Avalonia.Threading;
+using Ursa.Controls;
+
+namespace HeadlessTest.Ursa.Controls.AnchorTests;
+
+public class Tests
+{
+    [AvaloniaFact]
+    public async void Click_Anchor_With_Mouse_Should_Update_Scroll_Offset()
+    {
+        var window = new Window()
+        {
+            Width = 500,
+            Height = 500,
+        };
+        var view = new TestView();
+        window.Content = view;
+        window.Show();
+        
+        var anchor = view.FindControl<Anchor>("Anchor");
+        var scrollViewer = view.FindControl<ScrollViewer>("ScrollViewer");
+        var item4 = view.FindControl<AnchorItem>("Item4");
+        
+        Assert.NotNull(anchor);
+        Assert.NotNull(scrollViewer);
+        Assert.NotNull(item4);
+
+        var transltion = item4.TranslatePoint(new Point(0, 0), window);
+        
+        Assert.Equal(0, scrollViewer.Offset.Y);
+        
+        // Simulate a click on the anchor
+        window.MouseDown(new Point(10, transltion.Value.Y+10), MouseButton.Left);
+        Dispatcher.UIThread.RunJobs();
+        await Task.Delay(800);
+        Assert.True(item4.IsSelected);
+        Assert.Equal(300.0 * 3, scrollViewer.Offset.Y, 1.0);
+    }
+    
+    [AvaloniaFact]
+    public async void Change_Scroll_Offset_Should_Update_Selected_Item()
+    {
+        var window = new Window()
+        {
+            Width = 500,
+            Height = 500,
+        };
+        var view = new TestView();
+        window.Content = view;
+        window.Show();
+        
+        var anchor = view.FindControl<Anchor>("Anchor");
+        var scrollViewer = view.FindControl<ScrollViewer>("ScrollViewer");
+        var item1 = view.FindControl<AnchorItem>("Item1");
+        var item2 = view.FindControl<AnchorItem>("Item2");
+        var item4 = view.FindControl<AnchorItem>("Item4");
+        
+        Assert.NotNull(anchor);
+        Assert.NotNull(scrollViewer);
+        Assert.NotNull(item1);
+        Assert.NotNull(item2);
+        Assert.NotNull(item4);
+        
+        Dispatcher.UIThread.RunJobs();
+        
+        Assert.True(item1.IsSelected);
+        Assert.False(item2.IsSelected);
+
+        // Change the scroll offset
+        scrollViewer.Offset = new Vector(0, 310.0);
+        Dispatcher.UIThread.RunJobs();
+        
+        // Check if the second item is selected
+        Assert.True(item2.IsSelected);
+        Assert.False(item4.IsSelected);
+    }
+}