From 87217337b7fe82c9896b5a24217f35808d37e13a Mon Sep 17 00:00:00 2001
From: Misaki <misaki_39@outlook.com>
Date: Sat, 28 Mar 2026 12:45:55 +0900
Subject: [PATCH] fix(dock): encapsulate Children collection and polish tests

---
 .../Controls/Internal/Docking/DockGroupNode.cs       | 12 +++++++-----
 src/Test/Ghost.UnitTest/DockingModelTest.cs          |  3 +--
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockGroupNode.cs b/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockGroupNode.cs
index 909cbf3..f916fee 100644
--- a/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockGroupNode.cs
+++ b/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockGroupNode.cs
@@ -15,16 +15,19 @@ public partial class DockGroupNode : DockNode
     [ObservableProperty]
     public partial Orientation Orientation { get; set; }
 
+    private readonly ObservableCollection<DockNode> _children = new();
+
     /// <summary>
     /// Gets the collection of child nodes.
     /// </summary>
-    public ObservableCollection<DockNode> Children { get; } = new();
+    public ReadOnlyObservableCollection<DockNode> Children { get; }
 
     /// <summary>
     /// Initializes a new instance of the <see cref="DockGroupNode"/> class.
     /// </summary>
     public DockGroupNode()
     {
+        Children = new ReadOnlyObservableCollection<DockNode>(_children);
         Orientation = Orientation.Horizontal;
     }
 
@@ -35,7 +38,6 @@ public partial class DockGroupNode : DockNode
     /// <exception cref="ArgumentNullException">Thrown if node is null.</exception>
     /// <exception cref="InvalidOperationException">Thrown if adding the node would create a cycle or if adding self.</exception>
     public void AddChild(DockNode node)
-
     {
         ArgumentNullException.ThrowIfNull(node);
 
@@ -44,7 +46,7 @@ public partial class DockGroupNode : DockNode
             throw new InvalidOperationException("Cannot add a node to itself.");
         }
 
-        if (Children.Contains(node))
+        if (_children.Contains(node))
         {
             return;
         }
@@ -66,7 +68,7 @@ public partial class DockGroupNode : DockNode
         }
 
         node.Parent = this;
-        Children.Add(node);
+        _children.Add(node);
     }
 
     /// <summary>
@@ -75,7 +77,7 @@ public partial class DockGroupNode : DockNode
     /// <param name="node">The node to remove.</param>
     public void RemoveChild(DockNode node)
     {
-        if (Children.Remove(node))
+        if (_children.Remove(node))
         {
             node.Parent = null;
         }
diff --git a/src/Test/Ghost.UnitTest/DockingModelTest.cs b/src/Test/Ghost.UnitTest/DockingModelTest.cs
index b324619..3ce0018 100644
--- a/src/Test/Ghost.UnitTest/DockingModelTest.cs
+++ b/src/Test/Ghost.UnitTest/DockingModelTest.cs
@@ -1,5 +1,4 @@
 using Ghost.Editor.Core.Controls.Internal.Docking;
-using Microsoft.UI.Xaml.Controls;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace Ghost.UnitTest;
@@ -50,7 +49,7 @@ public class DockingModelTest
         {
             thrown = true;
         }
-        Assert.IsTrue(thrown);
+        Assert.IsTrue(thrown, "Should have thrown InvalidOperationException due to cycle.");
     }
 
     [TestMethod]