diff --git a/ILSpy.Tests/AssemblyList/AssemblyTreeTests.cs b/ILSpy.Tests/AssemblyList/AssemblyTreeTests.cs
index 0eb1b17cd..f9ad613dd 100644
--- a/ILSpy.Tests/AssemblyList/AssemblyTreeTests.cs
+++ b/ILSpy.Tests/AssemblyList/AssemblyTreeTests.cs
@@ -24,24 +24,20 @@ using System.Xml.Linq;
 
 using Avalonia;
 using Avalonia.Controls;
-using Avalonia.Controls.DataGridHierarchical;
 using Avalonia.Headless.NUnit;
 using Avalonia.Threading;
 using Avalonia.VisualTree;
 
 using AwesomeAssertions;
 
-using ICSharpCode.ILSpy.Properties;
-
 using ICSharpCode.Decompiler.TypeSystem;
+using ICSharpCode.ILSpy.Properties;
 using ICSharpCode.ILSpyX;
-using ICSharpCode.ILSpyX.TreeView;
 
 using ILSpy;
 using ILSpy.AppEnv;
 using ILSpy.AssemblyTree;
 using ILSpy.Commands;
-using ILSpy.Images;
 using ILSpy.TreeNodes;
 using ILSpy.ViewModels;
 using ILSpy.Views;
@@ -56,37 +52,49 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Assembly_Node_Has_Resources_Folder_When_Module_Has_Resources()
 	{
+		// Assemblies with embedded resources expose a "Resources" folder under the assembly
+		// node. Verifies the folder is present, contains entries, and every entry is an
+		// ILSpyTreeNode (typed factory routes specialised handlers, generic falls back to
+		// ResourceTreeNode — both are ILSpyTreeNodes).
+
+		// Arrange — boot, wait for assemblies.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
-		// Pick a loaded assembly that ships embedded resources. CoreLib always has at least
-		// the localised error-message tables.
+		// Act — pick CoreLib (always ships localised error-message tables), expand it.
 		var coreLibName = typeof(object).Assembly.GetName().Name!;
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(coreLibName);
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 
+		// Assert — exactly one Resources folder, named, non-empty, every child an ILSpyTreeNode.
 		var resources = assemblyNode.Children.OfType<ResourceListTreeNode>().Single();
 		resources.Text.Should().Be(Resources._Resources);
 		resources.EnsureLazyChildren();
+		resources.IsExpanded = true;
 		resources.Children.Should().NotBeEmpty();
-		// The factory dispatcher routes typed resources (.xml/.png/.ico/.cur/.xaml) to
-		// specialised ResourceEntryNode subclasses; everything else falls back to
-		// ResourceTreeNode. Both branches are ILSpyTreeNodes.
 		resources.Children.Should().AllBeAssignableTo<ILSpyTreeNode>();
 	}
 
 	[AvaloniaTest]
 	public async Task DataGrid_Has_Extended_Selection_Mode()
 	{
+		// The assembly tree DataGrid must run in Extended selection mode so users can
+		// Ctrl-click to multi-select rows.
+
+		// Arrange — boot, wait for assemblies + AssemblyListPane to materialise.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
+		// Act — locate the realised DataGrid inside the AssemblyListPane.
 		var pane = await window.WaitForComponent<AssemblyListPane>();
 		var treeGrid = await pane.WaitForComponent<DataGrid>();
+
+		// Assert — SelectionMode is Extended.
 		treeGrid.SelectionMode.Should().Be(DataGridSelectionMode.Extended,
 			"the assembly tree must let users Ctrl-click multiple rows");
 	}
@@ -94,6 +102,11 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Multi_Selection_Tracks_Multiple_Nodes_And_Marks_Them_IsSelected()
 	{
+		// Adding multiple nodes to AssemblyTreeModel.SelectedItems must reflect on each node's
+		// IsSelected flag (used by the tree view template binding) and removing one node must
+		// flip its IsSelected back without affecting siblings.
+
+		// Arrange — boot, wait for assemblies, expand Enumerable, grab two methods.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -102,20 +115,26 @@ public class AssemblyTreeTests
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
 		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var first = typeNode.Children.OfType<MethodTreeNode>()
 			.Single(m => m.MethodDefinition.Name == "AsEnumerable");
 		var second = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "Empty");
 
+		// Act 1 — add both nodes to the multi-selection.
 		vm.AssemblyTreeModel.SelectedItems.Add(first);
 		vm.AssemblyTreeModel.SelectedItems.Add(second);
 
+		// Assert 1 — both are tracked and both report IsSelected.
 		vm.AssemblyTreeModel.SelectedItems.Should().Contain(first);
 		vm.AssemblyTreeModel.SelectedItems.Should().Contain(second);
 		first.IsSelected.Should().BeTrue();
 		second.IsSelected.Should().BeTrue();
 
+		// Act 2 — remove one.
 		vm.AssemblyTreeModel.SelectedItems.Remove(first);
+
+		// Assert 2 — only the removed one flips back.
 		first.IsSelected.Should().BeFalse();
 		second.IsSelected.Should().BeTrue();
 	}
@@ -123,6 +142,11 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Loading_Zip_Package_Surfaces_Folders_And_Entries()
 	{
+		// Loading a .zip should run the bundled-archive file loader: nested directories become
+		// PackageFolderTreeNodes, top-level files become ResourceTreeNodes.
+
+		// Arrange — boot, wait for assemblies, build a fixture zip with a flat file + two
+		// folders containing one file each.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -141,6 +165,7 @@ public class AssemblyTreeTests
 				w.Write("<html />");
 		}
 
+		// Act — open the zip via the OpenCommand and wait for it to load.
 		var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
 		var openCommand = registry.Commands
 			.Single(c => c.Metadata.Header == nameof(Resources._Open))
@@ -156,7 +181,10 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(loaded.ShortName);
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 
+		// Assert — both nested folders show as PackageFolderTreeNodes; the flat file shows as
+		// a ResourceTreeNode with its original entry name.
 		var folderNames = assemblyNode.Children.OfType<PackageFolderTreeNode>()
 			.Select(f => (string)f.Text)
 			.ToList();
@@ -172,6 +200,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Dot_Resources_File_Resolves_To_ResourcesFileTreeNode()
 	{
+		// .resources entries get the dedicated ResourcesFileTreeNode handler, which exposes a
+		// string-table or inner ResourceEntryNode children (depending on payload type).
+
+		// Arrange — boot, wait for assemblies, expand CoreLib's Resources folder.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -180,15 +212,21 @@ public class AssemblyTreeTests
 		var coreLibName = typeof(object).Assembly.GetName().Name!;
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(coreLibName);
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 		var resources = assemblyNode.Children.OfType<ResourceListTreeNode>().Single();
 		resources.EnsureLazyChildren();
+		resources.IsExpanded = true;
 
+		// Act — look up the first .resources file and select it.
 		var resourceFileNode = resources.Children.OfType<ResourcesFileTreeNode>().FirstOrDefault();
 		((object?)resourceFileNode).Should().NotBeNull(
 			"CoreLib must ship at least one embedded .resources file");
 		resourceFileNode!.Resource.Name.Should().EndWith(".resources");
 
 		resourceFileNode.EnsureLazyChildren();
+
+		// Assert — either inner children or string-table entries — at least one branch must
+		// surface non-empty content.
 		(resourceFileNode.Children.Count > 0 || resourceFileNode.StringTableEntries.Count > 0)
 			.Should().BeTrue("a .resources file must surface either inner ResourceEntryNode children or string-table entries");
 	}
@@ -196,6 +234,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Assembly_Node_Has_References_Folder_Child()
 	{
+		// Each assembly node exposes a "References" folder child whose children are
+		// AssemblyReferenceTreeNodes — one per AssemblyRef row.
+
+		// Arrange — boot, wait for assemblies, expand System.Linq.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -203,11 +245,16 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 
+		// Act — find the References folder.
 		var refFolder = assemblyNode.Children.OfType<ReferenceFolderTreeNode>().Single();
+
+		// Assert — folder is named, expands to non-empty AssemblyReferenceTreeNode children.
 		refFolder.Text.Should().Be(Resources.References);
 
 		refFolder.EnsureLazyChildren();
+		refFolder.IsExpanded = true;
 		refFolder.Children.Should().NotBeEmpty();
 		refFolder.Children.Should().AllBeAssignableTo<AssemblyReferenceTreeNode>();
 	}
@@ -215,6 +262,13 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Assembly_Reference_Icon_Settles_To_Assembly_Once_Resolved()
 	{
+		// AssemblyReferenceTreeNode.Icon starts as the AssemblyLoading glyph and asynchronously
+		// flips to the resolved Assembly glyph once the resolver finishes — verifies the
+		// async-icon two-stage flow.
+
+		// Arrange — boot, wait for assemblies, force lazy children on assembly + References.
+		// Stay model-only (no IsExpanded = true) — visually expanding rows would render the
+		// icons, triggering the resolver and losing the lazy "loading" state we're asserting.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -228,18 +282,25 @@ public class AssemblyTreeTests
 		var refNode = refFolder.Children.OfType<AssemblyReferenceTreeNode>()
 			.First(n => n.AssemblyReference.Name == "System.Runtime");
 
-		// First access is "loading" — the resolver runs on the background dispatcher.
+		// Act 1 + Assert 1 — first access triggers the loading state.
 		var initialIcon = refNode.Icon;
 		initialIcon.Should().BeSameAs(global::ILSpy.Images.Images.AssemblyLoading);
 
+		// Act 2 — wait for resolver to finish.
 		await Waiters.WaitForAsync(() =>
 			!ReferenceEquals(refNode.Icon, global::ILSpy.Images.Images.AssemblyLoading));
+
+		// Assert 2 — icon settles on the resolved Assembly glyph.
 		refNode.Icon.Should().BeSameAs(global::ILSpy.Images.Images.Assembly);
 	}
 
 	[AvaloniaTest]
 	public async Task Assembly_Reference_Has_Referenced_Types_Subnode()
 	{
+		// Each AssemblyReferenceTreeNode contains a "Referenced Types" subnode that lists the
+		// TypeRef rows the host assembly imports from that reference.
+
+		// Arrange — boot, wait for assemblies, expand System.Linq → References → System.Runtime.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -247,16 +308,24 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 		var refFolder = assemblyNode.Children.OfType<ReferenceFolderTreeNode>().Single();
 		refFolder.EnsureLazyChildren();
+		refFolder.IsExpanded = true;
 
 		var refNode = refFolder.Children.OfType<AssemblyReferenceTreeNode>()
 			.First(n => n.AssemblyReference.Name == "System.Runtime");
 		refNode.EnsureLazyChildren();
+		refNode.IsExpanded = true;
 
+		// Act — find the ReferencedTypes subnode and expand it.
 		var typesNode = refNode.Children.OfType<AssemblyReferenceReferencedTypesTreeNode>().Single();
-		typesNode.Text.ToString().Should().Contain(Resources.ReferencedTypes);
 		typesNode.EnsureLazyChildren();
+		typesNode.IsExpanded = true;
+
+		// Assert — header text contains the expected label, and the children include at least
+		// one TypeReferenceTreeNode.
+		typesNode.Text.ToString().Should().Contain(Resources.ReferencedTypes);
 		typesNode.Children.Should().NotBeEmpty();
 		typesNode.Children.Should().Contain(c => c is TypeReferenceTreeNode);
 	}
@@ -264,6 +333,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task FindNamespaceNode_Returns_The_Tree_Node_For_A_Loaded_Namespace()
 	{
+		// AssemblyTreeNode.FindNamespaceNode is the lookup primitive used by navigation and
+		// search to land on a specific namespace.
+
+		// Arrange — boot, wait for assemblies, expand System.Linq.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -271,8 +344,12 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 
+		// Act — look up the System.Linq namespace.
 		var ns = assemblyNode.FindNamespaceNode("System.Linq");
+
+		// Assert — returns the actual NamespaceTreeNode child, not a clone.
 		((object?)ns).Should().NotBeNull();
 		ns!.Name.Should().Be("System.Linq");
 		assemblyNode.Children.OfType<NamespaceTreeNode>().Should().Contain(ns);
@@ -281,6 +358,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task FindTypeNode_Returns_The_Tree_Node_For_A_Loaded_Type()
 	{
+		// AssemblyTreeNode.FindTypeNode is the lookup primitive used by navigation and search
+		// to land on a specific type by ITypeDefinition.
+
+		// Arrange — boot, wait for assemblies, expand System.Linq.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -288,13 +369,17 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 
+		// Act — resolve System.Linq.Enumerable's ITypeDefinition, then look up its tree node.
 		var module = assemblyNode.LoadedAssembly.GetMetadataFileOrNull()!;
 		var typeSystem = (MetadataModule)module.GetTypeSystemOrNull()!.MainModule;
 		var enumerable = typeSystem.TopLevelTypeDefinitions
 			.First(t => t.ReflectionName == "System.Linq.Enumerable");
 
 		var node = assemblyNode.FindTypeNode(enumerable);
+
+		// Assert — non-null, with the matching metadata token.
 		((object?)node).Should().NotBeNull();
 		node!.Handle.Should().Be((System.Reflection.Metadata.TypeDefinitionHandle)enumerable.MetadataToken);
 	}
@@ -302,6 +387,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Member_Reference_Node_Uses_Method_Or_Field_Overlay_Icon()
 	{
+		// MemberReferenceTreeNode renders with an icon that overlays a "reference arrow" on
+		// top of the underlying Method/Field glyph — verifies that overlay routing works.
+
+		// Arrange — boot, wait for assemblies, expand System.Linq → References.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -309,23 +398,28 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 		var refFolder = assemblyNode.Children.OfType<ReferenceFolderTreeNode>().Single();
 		refFolder.EnsureLazyChildren();
+		refFolder.IsExpanded = true;
 
-		// Walk every reference's ReferencedTypes subtree until we find a TypeRef that
-		// has at least one MemberReference. System.Linq imports plenty (e.g. delegates,
-		// Func ctors) so this should always succeed.
+		// Act — walk every reference's ReferencedTypes subtree until we find a TypeRef with
+		// at least one MemberReference. System.Linq imports plenty (delegates, Func ctors)
+		// so this should always succeed.
 		MemberReferenceTreeNode? memberRefNode = null;
 		foreach (var refNode in refFolder.Children.OfType<AssemblyReferenceTreeNode>())
 		{
 			refNode.EnsureLazyChildren();
+			refNode.IsExpanded = true;
 			var typesNode = refNode.Children.OfType<AssemblyReferenceReferencedTypesTreeNode>().FirstOrDefault();
 			if (typesNode == null)
 				continue;
 			typesNode.EnsureLazyChildren();
+			typesNode.IsExpanded = true;
 			foreach (var typeRef in typesNode.Children.OfType<TypeReferenceTreeNode>())
 			{
 				typeRef.EnsureLazyChildren();
+				typeRef.IsExpanded = true;
 				memberRefNode = typeRef.Children.OfType<MemberReferenceTreeNode>().FirstOrDefault();
 				if (memberRefNode != null)
 					break;
@@ -334,6 +428,7 @@ public class AssemblyTreeTests
 				break;
 		}
 
+		// Assert — non-null, icon is one of the two ref glyphs, label is non-empty.
 		((object?)memberRefNode).Should().NotBeNull(
 			"at least one TypeRef under System.Linq's references must have member references");
 		memberRefNode!.Icon.Should().BeOneOf(global::ILSpy.Images.Images.MethodReference,
@@ -344,14 +439,16 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Exported_Type_Node_Uses_Export_Overlay_Icon()
 	{
+		// ExportedTypeTreeNode (type forwarders, e.g. mscorlib forwarding to
+		// System.Private.CoreLib) renders with the dedicated ExportedType glyph.
+
+		// Arrange — boot, wait for assemblies. Open mscorlib explicitly: it's the canonical
+		// type-forwarder facade and we need a known forwarder regardless of default startup.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
-		// `mscorlib` is the canonical type-forwarder facade: it reports ExportedTypes that
-		// resolve to System.Private.CoreLib. Open it explicitly so the test fixture has a
-		// loaded forwarder regardless of what the default startup list includes.
 		var coreLibDir = System.IO.Path.GetDirectoryName(typeof(object).Assembly.Location)!;
 		var mscorlibPath = System.IO.Path.Combine(coreLibDir, "mscorlib.dll");
 		if (!System.IO.File.Exists(mscorlibPath))
@@ -374,22 +471,28 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(loaded.ShortName);
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 		var refFolder = assemblyNode.Children.OfType<ReferenceFolderTreeNode>().Single();
 		refFolder.EnsureLazyChildren();
+		refFolder.IsExpanded = true;
 
+		// Act — walk every reference's ReferencedTypes for an ExportedTypeTreeNode.
 		ExportedTypeTreeNode? exportedNode = null;
 		foreach (var refNode in refFolder.Children.OfType<AssemblyReferenceTreeNode>())
 		{
 			refNode.EnsureLazyChildren();
+			refNode.IsExpanded = true;
 			var typesNode = refNode.Children.OfType<AssemblyReferenceReferencedTypesTreeNode>().FirstOrDefault();
 			if (typesNode == null)
 				continue;
 			typesNode.EnsureLazyChildren();
+			typesNode.IsExpanded = true;
 			exportedNode = typesNode.Children.OfType<ExportedTypeTreeNode>().FirstOrDefault();
 			if (exportedNode != null)
 				break;
 		}
 
+		// Assert — non-null, uses the ExportedType glyph, label is non-empty.
 		((object?)exportedNode).Should().NotBeNull(
 			"mscorlib must forward types to System.Private.CoreLib via ExportedType rows");
 		exportedNode!.Icon.Should().BeSameAs(global::ILSpy.Images.Images.ExportedType);
@@ -399,6 +502,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Expanding_Assembly_Reference_Reveals_Transitive_References()
 	{
+		// AssemblyReferenceTreeNode shows the reference's *own* AssemblyRef rows as children
+		// — building a transitive reference tree the user can drill into.
+
+		// Arrange — boot, wait for assemblies, expand System.Linq → References.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -406,27 +513,36 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 		var refFolder = assemblyNode.Children.OfType<ReferenceFolderTreeNode>().Single();
 		refFolder.EnsureLazyChildren();
+		refFolder.IsExpanded = true;
 
-		// Many BCL refs resolve to facade assemblies with zero transitive references; iterate
-		// until we find one that has its own AssemblyRefs to verify the transitive walk works.
+		// Act — many BCL refs resolve to facade assemblies with zero transitive references;
+		// iterate until we find one that has its own AssemblyRefs.
 		bool foundTransitive = false;
 		foreach (var refNode in refFolder.Children.OfType<AssemblyReferenceTreeNode>())
 		{
 			refNode.EnsureLazyChildren();
+			refNode.IsExpanded = true;
 			if (refNode.Children.OfType<AssemblyReferenceTreeNode>().Any())
 			{
 				foundTransitive = true;
 				break;
 			}
 		}
+
+		// Assert — at least one reference exposes its own AssemblyRefs.
 		foundTransitive.Should().BeTrue("at least one reference must expose its own AssemblyRefs as child nodes");
 	}
 
 	[AvaloniaTest]
 	public async Task Activating_Assembly_Reference_Selects_Resolved_Assembly_Node()
 	{
+		// Double-clicking (Activate) an AssemblyReferenceTreeNode should jump to the resolved
+		// assembly's AssemblyTreeNode in the tree — auto-loading it if necessary.
+
+		// Arrange — boot, wait for assemblies, expand System.Linq → References.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -434,15 +550,19 @@ public class AssemblyTreeTests
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 		var refFolder = assemblyNode.Children.OfType<ReferenceFolderTreeNode>().Single();
 		refFolder.EnsureLazyChildren();
+		refFolder.IsExpanded = true;
 
 		var refNode = refFolder.Children.OfType<AssemblyReferenceTreeNode>()
 			.Single(n => n.AssemblyReference.Name == "System.Runtime");
 
+		// Act — fire ActivateItem with a stub event-args so we can assert handled.
 		var args = new StubRoutedEventArgs();
 		refNode.ActivateItem(args);
 
+		// Assert — args.Handled flips and the selection lands on the resolved assembly node.
 		args.Handled.Should().BeTrue();
 		await Waiters.WaitForAsync(() =>
 			vm.AssemblyTreeModel.SelectedItem is AssemblyTreeNode selected
@@ -457,6 +577,12 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Selecting_Method_Auto_Loads_Referenced_Assemblies()
 	{
+		// Decompiling a method whose body references types from currently-unloaded assemblies
+		// must auto-load those assemblies (so the decompiler can resolve them) — and the
+		// auto-loaded entries must be flagged IsAutoLoaded.
+
+		// Arrange — boot, wait for assemblies, open System.Net.Http (its CancelPendingRequests
+		// pulls in plenty of currently-unreferenced types).
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -481,9 +607,12 @@ public class AssemblyTreeTests
 			.Select(a => a.FileName)
 			.ToHashSet(System.StringComparer.OrdinalIgnoreCase);
 
+		// Act — select CancelPendingRequests, wait for decompile, then for new (auto-loaded)
+		// assemblies to appear.
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			loaded.ShortName, "System.Net.Http", "System.Net.Http.HttpClient");
 		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var methodNode = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "CancelPendingRequests");
 
@@ -493,6 +622,8 @@ public class AssemblyTreeTests
 		await Waiters.WaitForAsync(() =>
 			vm.AssemblyTreeModel.AssemblyList!.GetAssemblies().Any(a => !initialFiles.Contains(a.FileName)));
 
+		// Assert — non-empty set of newly-loaded entries, all flagged IsAutoLoaded both on
+		// LoadedAssembly and on the matching tree node.
 		var addedAssemblies = vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
 			.Where(a => !initialFiles.Contains(a.FileName))
 			.ToList();
@@ -509,6 +640,11 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Auto_Loaded_Assemblies_Are_Not_Persisted()
 	{
+		// Auto-loaded assemblies are an artefact of an in-flight decompile, not of the user's
+		// curated list — saving the assembly list must omit them while keeping the ones the
+		// user actually opened.
+
+		// Arrange — boot, wait for assemblies, open + select a method that triggers auto-load.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -532,6 +668,7 @@ public class AssemblyTreeTests
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			loaded.ShortName, "System.Net.Http", "System.Net.Http.HttpClient");
 		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var methodNode = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "CancelPendingRequests");
 
@@ -541,6 +678,8 @@ public class AssemblyTreeTests
 		await Waiters.WaitForAsync(() =>
 			vm.AssemblyTreeModel.AssemblyList!.GetAssemblies().Any(a => a.IsAutoLoaded));
 
+		// Act — save the assembly list to disk, then read the file back and tally the persisted
+		// FileName entries.
 		var settingsService = AppComposition.Current.GetExport<SettingsService>();
 		var manager = settingsService.AssemblyListManager;
 		manager.SaveList(vm.AssemblyTreeModel.AssemblyList!);
@@ -551,6 +690,7 @@ public class AssemblyTreeTests
 			.Select(e => e.Value)
 			.ToHashSet(System.StringComparer.OrdinalIgnoreCase);
 
+		// Assert — every IsAutoLoaded assembly was omitted; every manual one is present.
 		var assemblies = vm.AssemblyTreeModel.AssemblyList!.GetAssemblies();
 		var autoLoaded = assemblies.Where(a => a.IsAutoLoaded).ToList();
 		autoLoaded.Should().NotBeEmpty();
@@ -565,6 +705,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Opening_Assembly_Adds_It_To_The_Tree()
 	{
+		// OpenCommand must add the freshly-opened assembly to the AssemblyList, materialise a
+		// matching tree node, and select that node so the user sees their newly-opened file.
+
+		// Arrange — boot, wait for assemblies, snapshot the initial count.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -573,6 +717,7 @@ public class AssemblyTreeTests
 		var newAsmPath = typeof(System.Net.Http.HttpClient).Assembly.Location;
 		var initialCount = vm.AssemblyTreeModel.AssemblyList!.Count;
 
+		// Act — fire OpenCommand on a new path and wait for the load to complete.
 		var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
 		var openCommand = registry.Commands
 			.Single(c => c.Metadata.Header == nameof(Resources._Open))
@@ -587,6 +732,8 @@ public class AssemblyTreeTests
 			.First(a => string.Equals(a.FileName, newAsmPath, System.StringComparison.OrdinalIgnoreCase));
 		await loaded.GetLoadResultAsync();
 
+		// Assert — count incremented by one; the corresponding tree node points at the
+		// freshly-loaded assembly and is selected.
 		vm.AssemblyTreeModel.AssemblyList!.Count.Should().Be(initialCount + 1);
 		var node = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(loaded.ShortName);
 		node.LoadedAssembly.Should().BeSameAs(loaded);
@@ -596,6 +743,13 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task User_Click_On_Visible_Row_Does_Not_Recentre_Viewport()
 	{
+		// CenterRowInView must skip the recentre when the clicked row is already fully visible.
+		// Regression test: the original implementation used a clickInProgress flag that fired
+		// during file picker await/resume, dragging the viewport on every click. The fix is an
+		// in-viewport early-return.
+
+		// Arrange — boot, wait for assemblies, expand a sub-tree large enough to scroll. Park
+		// the viewport mid-list so clicks are at non-zero offset.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -604,17 +758,19 @@ public class AssemblyTreeTests
 		var enumerable = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
 		enumerable.EnsureLazyChildren();
+		enumerable.IsExpanded = true;
 		var ns = (NamespaceTreeNode)enumerable.Parent!;
 		ns.EnsureLazyChildren();
+		ns.IsExpanded = true;
 		foreach (var child in ns.Children.OfType<TypeTreeNode>())
+		{
 			child.EnsureLazyChildren();
+			child.IsExpanded = true;
+		}
 
 		var pane = await window.WaitForComponent<AssemblyListPane>();
 		var grid = await pane.WaitForComponent<DataGrid>();
 
-		// Park the viewport mid-list so the next-clicked row sits at a non-zero offset. The
-		// regression would re-centre on click and snap the offset back; we want offset to
-		// stay put.
 		vm.AssemblyTreeModel.SelectedItem = enumerable;
 		await Waiters.WaitForAsync(() => ReferenceEquals(vm.AssemblyTreeModel.SelectedItem, enumerable));
 		for (int i = 0; i < 8; i++)
@@ -633,9 +789,9 @@ public class AssemblyTreeTests
 		scrollViewer.Offset.Y.Should().BeGreaterThan(5,
 			"the test scenario requires the viewport be parked mid-list");
 
-		// Pick a different visible row to click on; clicking an already-visible row must NOT
-		// move the viewport. Use the *bottom-most* visible row for a strict check — if the bug
-		// regressed, CenterRowInView would scroll it up to the middle and offset would change.
+		// Pick the bottom-most visible non-selected row — that's the strictest probe. If the
+		// bug regressed, CenterRowInView would scroll it up to the middle and offset would
+		// change.
 		var candidateRow = grid.GetVisualDescendants().OfType<DataGridRow>()
 			.Where(r => !r.IsSelected
 				&& r.TranslatePoint(new Point(0, 0), scrollViewer) is { } p
@@ -646,7 +802,7 @@ public class AssemblyTreeTests
 
 		var offsetBefore = scrollViewer.Offset.Y;
 
-		// Real pointer click — setting SelectedItem programmatically would fire DataGrid's
+		// Act — real pointer click. Setting SelectedItem programmatically would fire DataGrid's
 		// internal ScrollIntoView too, which a real user click does not.
 		var rowCentre = candidateRow!.TranslatePoint(
 			new Point(candidateRow.Bounds.Width / 2, candidateRow.Bounds.Height / 2),
@@ -660,6 +816,7 @@ public class AssemblyTreeTests
 			await Task.Delay(25);
 		}
 
+		// Assert — viewport offset is unchanged (within 1px tolerance for layout jitter).
 		scrollViewer.Offset.Y.Should().BeApproximately(offsetBefore, 1.0,
 			"clicking an already-visible row must not move the viewport");
 	}
@@ -667,6 +824,10 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Save_Code_Command_Dispatches_Single_Selected_Node_Save_Override()
 	{
+		// SaveCommand on a single ILSpyTreeNode selection must call the node's own Save()
+		// method — that's how nodes (e.g. resources) opt into a custom save dialog/format.
+
+		// Arrange — boot, wait for assemblies, plant a probe node that records when Save runs.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -675,12 +836,14 @@ public class AssemblyTreeTests
 		var probe = new SaveProbeNode();
 		vm.AssemblyTreeModel.SelectedItem = probe;
 
+		// Act — fire the Save Code main-menu command.
 		var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
 		var saveCmd = registry.Commands
 			.Single(c => c.Metadata.Header == nameof(Resources._SaveCode))
 			.CreateExport().Value;
 		saveCmd.Execute(null);
 
+		// Assert — probe's Save() ran.
 		probe.SaveCalled.Should().BeTrue(
 			"Save Code on a single ILSpyTreeNode selection must dispatch through ILSpyTreeNode.Save()");
 	}
@@ -699,6 +862,11 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Save_Code_Command_Writes_Full_Decompilation_To_Picked_Path()
 	{
+		// When SaveCommand falls through (no node-specific Save override), it must run a full
+		// decompilation (DecompilationOptions.FullDecompilation = true) of the selection and
+		// write the resulting C# to the user-picked path.
+
+		// Arrange — boot, wait for assemblies, select a method, wait for the in-tab decompile.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -707,11 +875,14 @@ public class AssemblyTreeTests
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
 		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var method = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "AsEnumerable");
 		vm.AssemblyTreeModel.SelectedItem = method;
 		await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Act — invoke SaveCodeAsync with a temp path (bypassing the file picker so the test
+		// is deterministic).
 		var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
 		var saveCmd = (global::ILSpy.Commands.SaveCommand)registry.Commands
 			.Single(c => c.Metadata.Header == nameof(Resources._SaveCode))
@@ -724,6 +895,8 @@ public class AssemblyTreeTests
 		{
 			await saveCmd.SaveCodeAsync(tempFile);
 
+			// Assert — file exists; contents include the method name and a body fragment that
+			// only appears with FullDecompilation = true.
 			System.IO.File.Exists(tempFile).Should().BeTrue();
 			var contents = await System.IO.File.ReadAllTextAsync(tempFile);
 			contents.Should().Contain("AsEnumerable",
@@ -741,12 +914,16 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Delete_Key_On_Selected_Assembly_Unloads_It_From_The_List()
 	{
+		// Pressing Del on a selected AssemblyTreeNode must unload that assembly from the
+		// AssemblyList while leaving siblings intact.
+
+		// Arrange — boot, wait for assemblies, pick the assembly to evict + a sibling we
+		// expect to survive, select the sacrificial one, focus the grid.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
-		// Pick the assembly we'll evict + a sibling we expect to survive.
 		var sacrificialName = typeof(System.Linq.Enumerable).Assembly.GetName().Name!;
 		var survivorName = typeof(object).Assembly.GetName().Name!;
 		var sacrificialNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(sacrificialName);
@@ -758,7 +935,8 @@ public class AssemblyTreeTests
 		grid.Focus();
 		Dispatcher.UIThread.RunJobs();
 
-		// Headless keyboard event — simulates the user pressing Del while the tree has focus.
+		// Act — headless keyboard event simulating the user pressing Del while the tree has
+		// focus.
 		global::Avalonia.Headless.HeadlessWindowExtensions.KeyPress(
 			window,
 			global::Avalonia.Input.Key.Delete,
@@ -766,6 +944,7 @@ public class AssemblyTreeTests
 			global::Avalonia.Input.PhysicalKey.Delete,
 			null);
 
+		// Assert — the sacrificial assembly is gone from the list; the survivor remains.
 		await Waiters.WaitForAsync(() =>
 			!vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
 				.Any(a => string.Equals(a.ShortName, sacrificialName, System.StringComparison.Ordinal)));
@@ -778,12 +957,16 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Clear_Assembly_List_Command_Empties_The_Active_List()
 	{
+		// The Clear Assembly List menu command must drop every entry from the active list.
+
+		// Arrange — boot, wait for assemblies, baseline the non-empty count.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 		vm.AssemblyTreeModel.AssemblyList!.Count.Should().BeGreaterThan(0);
 
+		// Act — fire the Clear command.
 		var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
 		var clearCmd = registry.Commands
 			.Single(c => c.Metadata.Header == nameof(Resources.ClearAssemblyList))
@@ -791,6 +974,7 @@ public class AssemblyTreeTests
 		clearCmd.CanExecute(null).Should().BeTrue("non-empty list must enable Clear");
 		clearCmd.Execute(null);
 
+		// Assert — the list goes to zero entries.
 		await Waiters.WaitForAsync(() => vm.AssemblyTreeModel.AssemblyList!.Count == 0);
 		vm.AssemblyTreeModel.AssemblyList!.Count.Should().Be(0);
 	}
@@ -798,13 +982,17 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Remove_Assemblies_With_Load_Errors_Drops_Only_Broken_Entries()
 	{
+		// The "Remove Assemblies with Load Errors" command must drop every entry whose load
+		// failed — and *only* those, leaving valid assemblies in place.
+
+		// Arrange — boot, wait for assemblies, plant a "broken" entry: a real file that isn't
+		// a PE binary. AssemblyList records it but the load fails — that's the state the
+		// command targets.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
-		// Add a "broken" assembly: a real file that isn't a PE binary. AssemblyList records
-		// it but the load fails — that's exactly the state the command targets.
 		var brokenPath = System.IO.Path.Combine(
 			System.IO.Path.GetTempPath(),
 			"ilspy-bogus-" + System.Guid.NewGuid().ToString("N") + ".dll");
@@ -826,6 +1014,7 @@ public class AssemblyTreeTests
 				.ToList();
 			validBefore.Should().NotBeEmpty("at least one real assembly must remain to verify it's spared");
 
+			// Act — fire the command.
 			var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
 			var cmd = registry.Commands
 				.Single(c => c.Metadata.Header == nameof(Resources._RemoveAssembliesWithLoadErrors))
@@ -837,6 +1026,7 @@ public class AssemblyTreeTests
 				!vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
 					.Any(a => string.Equals(a.FileName, brokenPath, System.StringComparison.OrdinalIgnoreCase)));
 
+			// Assert — broken path gone; every previously-valid path still present.
 			var remaining = vm.AssemblyTreeModel.AssemblyList!.GetAssemblies().Select(a => a.FileName).ToList();
 			remaining.Should().NotContain(brokenPath, "the broken assembly should be removed");
 			foreach (var path in validBefore)
@@ -852,6 +1042,13 @@ public class AssemblyTreeTests
 	[AvaloniaTest]
 	public async Task Setting_SharpTreeNode_IsExpanded_Expands_Row_In_Grid()
 	{
+		// ProDataGrid's HierarchicalOptions.IsExpandedPropertyPath wires SharpTreeNode.IsExpanded
+		// to the grid's wrapper expansion state via reflection + INotifyPropertyChanged. Setting
+		// IsExpanded on the model must propagate to the grid wrapper without any manual
+		// subscription bookkeeping.
+
+		// Arrange — boot, wait for assemblies, locate the realised DataGrid and the
+		// HierarchicalModel wrapper for the assembly node.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -861,22 +1058,23 @@ public class AssemblyTreeTests
 		var grid = await pane.WaitForComponent<DataGrid>();
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
-		// Before: grid wrapper for assemblyNode must exist and not be expanded.
 		var hm = (global::Avalonia.Controls.DataGridHierarchical.IHierarchicalModel)grid.HierarchicalModel!;
 		var hNode = hm.FindNode(assemblyNode);
 		hNode.Should().NotBeNull();
 		hNode!.IsExpanded.Should().BeFalse("baseline: top-level assembly rows start collapsed");
 
-		// Production-shaped action: just toggle the model property. ProDataGrid's
-		// HierarchicalOptions.IsExpandedPropertyPath observes INPC and pushes to the wrapper.
+		// Act — production-shaped action: just toggle the model property.
+		assemblyNode.EnsureLazyChildren();
 		assemblyNode.IsExpanded = true;
 
+		// Drain the dispatcher so the wiring (PropertyChanged → hm.Expand) settles.
 		for (int i = 0; i < 5; i++)
 		{
 			Dispatcher.UIThread.RunJobs();
 			await Task.Delay(20);
 		}
 
+		// Assert — the grid wrapper now reports IsExpanded == true.
 		hm.FindNode(assemblyNode)!.IsExpanded.Should().BeTrue(
 			"setting SharpTreeNode.IsExpanded must propagate to the HierarchicalModel wrapper");
 	}
diff --git a/ILSpy.Tests/Editor/DecompilerViewTests.cs b/ILSpy.Tests/Editor/DecompilerViewTests.cs
index 8fe945364..4ff64b99a 100644
--- a/ILSpy.Tests/Editor/DecompilerViewTests.cs
+++ b/ILSpy.Tests/Editor/DecompilerViewTests.cs
@@ -45,6 +45,11 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Selecting_AsEnumerable_Method_Decompiles_Into_Document_View()
 	{
+		// Selecting a MethodTreeNode in the assembly tree must trigger a decompile and the
+		// resulting C# (signature + body) must land in the document tab. Also verifies the
+		// row scrolls into view (CenteredInView assertion) so the user sees the selection.
+
+		// Arrange — boot the window, wait for assemblies, expand Enumerable, locate AsEnumerable.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -52,13 +57,16 @@ public class DecompilerViewTests
 
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var methodNode = typeNode.Children.OfType<MethodTreeNode>()
 			.Single(m => m.MethodDefinition.Name == "AsEnumerable");
 		methodNode.MethodDefinition.IsExtensionMethod.Should().BeTrue();
 
+		// Act — select the method node and wait for the decompile.
 		vm.AssemblyTreeModel.SelectedItem = methodNode;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+
+		// Assert — signature + body fragments are present and the row centred in the tree.
 		tab.Text.Should().Contain("AsEnumerable");
 		tab.Text.Should().Contain("IEnumerable<TSource>");
 		tab.Text.Should().Contain("return source");
@@ -69,18 +77,25 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Selecting_References_Folder_Decompiles_References_Listing()
 	{
+		// The References folder under each assembly is a synthetic node; selecting it emits a
+		// summary listing (target framework, runtime pack, referenced assemblies, load log)
+		// rather than decompiled C#.
+
+		// Arrange — boot, wait for assemblies, expand the System.Linq assembly node.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
-		assemblyNode.EnsureLazyChildren();
+		assemblyNode.IsExpanded = true;
 		var refFolder = assemblyNode.Children.OfType<ReferenceFolderTreeNode>().Single();
 
+		// Act — select the References folder and wait for its decompile output.
 		vm.AssemblyTreeModel.SelectedItem = refFolder;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Assert — every header and a representative referenced assembly land in the listing.
 		tab.Text.Should().Contain("Detected TargetFramework-Id:");
 		tab.Text.Should().Contain("Detected RuntimePack:");
 		tab.Text.Should().Contain("Referenced assemblies (in metadata order):");
@@ -91,6 +106,10 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Selecting_Type_Node_Decompiles_Type_Definition()
 	{
+		// Selecting a TypeTreeNode (System.Version) must decompile the full class declaration
+		// including representative members.
+
+		// Arrange — boot, wait for assemblies, find System.Version.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -100,9 +119,11 @@ public class DecompilerViewTests
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			coreLib, "System", "System.Version");
 
+		// Act — select the type node, wait for the decompile.
 		vm.AssemblyTreeModel.SelectedItem = typeNode;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Assert — class declaration + representative property names land in the output.
 		tab.Text.Should().Contain("class Version");
 		tab.Text.Should().Contain("Major");
 		tab.Text.Should().Contain("Minor");
@@ -111,6 +132,10 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Selecting_Property_Node_Decompiles_Property()
 	{
+		// PropertyTreeNode → just the single property's declaration (with type prefix), not
+		// the full enclosing class.
+
+		// Arrange — boot, wait for assemblies, expand System.Version, grab Major.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -119,19 +144,25 @@ public class DecompilerViewTests
 		var coreLib = typeof(object).Assembly.GetName().Name!;
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			coreLib, "System", "System.Version");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var propertyNode = typeNode.Children.OfType<PropertyTreeNode>()
 			.Single(p => p.PropertyDefinition.Name == "Major");
 
+		// Act — select the property, wait for the decompile.
 		vm.AssemblyTreeModel.SelectedItem = propertyNode;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Assert — property declaration lands in the output.
 		tab.Text.Should().Contain("public int Major");
 	}
 
 	[AvaloniaTest]
 	public async Task Selecting_Field_Node_Decompiles_Field()
 	{
+		// FieldTreeNode (System.Math.PI) → decompiled field declaration with its constant
+		// initializer.
+
+		// Arrange — boot, wait for assemblies, expand System.Math, grab PI.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -140,13 +171,15 @@ public class DecompilerViewTests
 		var coreLib = typeof(object).Assembly.GetName().Name!;
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			coreLib, "System", "System.Math");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var fieldNode = typeNode.Children.OfType<FieldTreeNode>()
 			.Single(f => f.FieldDefinition.Name == "PI");
 
+		// Act — select the field, wait for the decompile.
 		vm.AssemblyTreeModel.SelectedItem = fieldNode;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Assert — declaration and constant value both land.
 		tab.Text.Should().Contain("public const double PI");
 		tab.Text.Should().Contain("3.14159");
 	}
@@ -154,6 +187,9 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Selecting_Event_Node_Decompiles_Event()
 	{
+		// EventTreeNode (AppDomain.ProcessExit) → decompiled event declaration.
+
+		// Arrange — boot, wait for assemblies, expand AppDomain, grab ProcessExit.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -162,13 +198,15 @@ public class DecompilerViewTests
 		var coreLib = typeof(object).Assembly.GetName().Name!;
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			coreLib, "System", "System.AppDomain");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var eventNode = typeNode.Children.OfType<EventTreeNode>()
 			.Single(e => e.EventDefinition.Name == "ProcessExit");
 
+		// Act — select the event, wait for the decompile.
 		vm.AssemblyTreeModel.SelectedItem = eventNode;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Assert — event keyword + name land in the output.
 		tab.Text.Should().Contain("event EventHandler");
 		tab.Text.Should().Contain("ProcessExit");
 	}
@@ -176,6 +214,9 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Selecting_Namespace_Node_Decompiles_Namespace()
 	{
+		// NamespaceTreeNode → decompiled namespace contents (the small types it contains).
+
+		// Arrange — boot, wait for assemblies, locate System.Runtime.Versioning.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -185,9 +226,11 @@ public class DecompilerViewTests
 		var namespaceNode = vm.AssemblyTreeModel.FindNode<NamespaceTreeNode>(
 			coreLib, "System.Runtime.Versioning");
 
+		// Act — select the namespace, wait for the decompile.
 		vm.AssemblyTreeModel.SelectedItem = namespaceNode;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Assert — representative type names land in the output.
 		tab.Text.Should().Contain("TargetFrameworkAttribute");
 		tab.Text.Should().Contain("SupportedOSPlatformAttribute");
 	}
@@ -195,14 +238,18 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Decompiler_Tab_Title_Tracks_Tree_Node_Text_When_Node_Loads_Late()
 	{
+		// Opening a fresh assembly via OpenCommand selects it before LoadedAssembly.Text has
+		// the full "(version, tfm)" suffix wired up. The tab title used to lock in the bare
+		// ShortName at that moment; it must instead update once Text becomes available.
+
+		// Arrange — boot, wait for assemblies.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
-		// Open a fresh assembly via the command and immediately let the OpenCommand select it,
-		// before LoadedAssembly.Text has the rich "(version, tfm)" suffix wired up. This is the
-		// timing window where the tab title used to lock in the bare ShortName.
+		// Act 1 — fire OpenCommand on a new path. OpenCommand selects the new node before its
+		// rich Text (with version + tfm) settles, exercising the late-update path.
 		var newAsmPath = typeof(System.Net.Http.HttpClient).Assembly.Location;
 		var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
 		var openCommand = registry.Commands
@@ -214,10 +261,13 @@ public class DecompilerViewTests
 			vm.AssemblyTreeModel.SelectedItem is AssemblyTreeNode n
 				&& string.Equals(n.LoadedAssembly.FileName, newAsmPath, System.StringComparison.OrdinalIgnoreCase));
 
+		// Act 2 — wait for the rich form of LoadedAssembly.Text to materialise.
 		var node = (AssemblyTreeNode)vm.AssemblyTreeModel.SelectedItem!;
 		await node.LoadedAssembly.GetLoadResultAsync();
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
+		// Assert — once Text is rich, the tab title catches up. Sanity-check the form is rich
+		// (otherwise the test isn't exercising the late-update path).
 		await Waiters.WaitForAsync(() => string.Equals(tab.Title, node.Text?.ToString(), System.StringComparison.Ordinal));
 		node.Text!.ToString().Should().NotBe(node.LoadedAssembly.ShortName,
 			"the rich form (with version + tfm) must be available, otherwise the test isn't exercising the late-update path");
@@ -227,6 +277,12 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Decompile_Tab_Title_Cycles_Round_Spinner_While_Decompiling()
 	{
+		// While a decompile is in flight the tab title should prefix with one of ten Braille
+		// spinner glyphs so the user sees activity. The editor's Text must NOT receive the
+		// glyph (only the title bar). Once decompilation finishes, the glyph clears.
+
+		// Arrange — boot, wait for assemblies, run an initial decompile so the second selection
+		// produces a real "in flight" period (not the cold-start one).
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -240,6 +296,7 @@ public class DecompilerViewTests
 		var editorTexts = new List<string>();
 		tab.PropertyChanged += OnTabPropertyChanged;
 
+		// Act — kick off a second decompile and observe Title/Text changes throughout.
 		var coreLib = typeof(object).Assembly.GetName().Name!;
 		var second = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(coreLib, "System", "System.Version");
 		vm.AssemblyTreeModel.SelectedItem = second;
@@ -247,6 +304,8 @@ public class DecompilerViewTests
 
 		tab.PropertyChanged -= OnTabPropertyChanged;
 
+		// Assert — at least one captured title contained a spinner glyph; no editor Text ever
+		// did; the final title is glyph-free.
 		var glyphs = new[] { '⠋', '⠙', '⠹', '⠸', '⠼', '⠴', '⠦', '⠧', '⠇', '⠏' };
 		titles.Should().Contain(t => glyphs.Any(t.Contains),
 			"the tab title must show one of the Braille spinner frames while decompilation is in flight");
@@ -267,6 +326,10 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Multi_Selection_Tab_Title_Joins_All_Selected_Names_With_Comma()
 	{
+		// Selecting several nodes via Ctrl+Click feeds them all into one decompile. The tab
+		// title must list every selected node's display text comma-joined.
+
+		// Arrange — boot, wait for assemblies, expand Enumerable, grab two methods.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -274,23 +337,30 @@ public class DecompilerViewTests
 
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var asEnumerable = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "AsEnumerable");
 		var empty = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "Empty");
 
+		// Act — replace the selection with both nodes.
 		vm.AssemblyTreeModel.SelectedItems.Clear();
 		vm.AssemblyTreeModel.SelectedItems.Add(asEnumerable);
 		vm.AssemblyTreeModel.SelectedItems.Add(empty);
 
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+
+		// Assert — title is the two display texts joined with ", ".
 		tab.Title.Should().Be($"{asEnumerable.Text}, {empty.Text}");
 	}
 
 	[AvaloniaTest]
 	public async Task Multi_Selecting_Methods_Decompiles_All_Of_Them_Into_One_View()
 	{
+		// Multi-selection isn't just a title concern — both methods' bodies must actually be
+		// decompiled into one combined document.
+
+		// Arrange — boot, wait for assemblies, expand Enumerable, grab two methods.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -298,35 +368,46 @@ public class DecompilerViewTests
 
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var asEnumerable = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "AsEnumerable");
 		var empty = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "Empty");
 
+		// Act — multi-select the two methods.
 		vm.AssemblyTreeModel.SelectedItems.Clear();
 		vm.AssemblyTreeModel.SelectedItems.Add(asEnumerable);
 		vm.AssemblyTreeModel.SelectedItems.Add(empty);
 
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+
+		// Assert — both names AND a body-fragment from one of them confirm both bodies
+		// actually rendered (not just signatures).
 		tab.Text.Should().Contain("AsEnumerable");
 		tab.Text.Should().Contain("Empty");
-		// Body fragment from AsEnumerable to confirm both bodies actually rendered.
 		tab.Text.Should().Contain("return source");
 	}
 
 	[AvaloniaTest]
 	public async Task Selecting_Assembly_Node_Emits_Header_And_Assembly_Attributes()
 	{
+		// AssemblyTreeNode → emit a "manifest"-style summary header (file, identity, runtime,
+		// architecture, global type) plus the assembly-level attributes block.
+
+		// Arrange — boot, wait for assemblies, find System.Linq.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
+
+		// Act — select the assembly node, wait for the decompile.
 		vm.AssemblyTreeModel.SelectedItem = assemblyNode;
 
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+
+		// Assert — every documented header line and at least one assembly attribute land.
 		tab.Text.Should().Contain("// " + assemblyNode.LoadedAssembly.FileName);
 		tab.Text.Should().Contain("// System.Linq, Version=");
 		tab.Text.Should().Contain("// Global type: <Module>");
@@ -338,18 +419,23 @@ public class DecompilerViewTests
 	[AvaloniaTest]
 	public async Task Xml_Resource_Installs_FoldingManager_With_Folds()
 	{
+		// XmlResourceEntryNode bumps the editor into XML mode (SyntaxExtension=".xml"), and
+		// DecompilerTextView.ApplyDocument must wire AvaloniaEdit's XmlFoldingStrategy so
+		// multi-line elements become collapsible.
+
+		// Arrange — boot, wait for assemblies, seed the decompiler tab with an assembly view
+		// so the document/editor wiring is realised.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
 		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
 
-		// Seed the decompiler tab.
 		var assemblyNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		vm.AssemblyTreeModel.SelectedItem = assemblyNode;
 		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
-		// Drop in a synthetic XML resource. XmlResourceEntryNode → SyntaxExtension=".xml" →
-		// DecompilerTextView.ApplyDocument runs XmlFoldingStrategy.
+		// Act — drop a synthetic XML resource into the tab. XmlResourceEntryNode triggers
+		// SyntaxExtension=".xml" and the XmlFoldingStrategy install.
 		var xml = "<root>\n  <child attr=\"v\">\n    text\n  </child>\n  <other>\n  </other>\n</root>";
 		var bytes = System.Text.Encoding.UTF8.GetBytes(xml);
 		tab.CurrentNode = new XmlResourceEntryNode("test.xml", () => new System.IO.MemoryStream(bytes));
@@ -363,8 +449,8 @@ public class DecompilerViewTests
 			await Task.Delay(20);
 		}
 
-		// FoldingManager is held in a private field — reflection is the lightest probe; a
-		// public accessor purely for tests would leak detail.
+		// Assert — FoldingManager is installed (private field, reflected) and produced fold
+		// ranges for the multi-line elements.
 		var fmField = typeof(DecompilerTextView).GetField("activeFoldingManager",
 			System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
 		fmField.Should().NotBeNull();
diff --git a/ILSpy.Tests/MainWindow/MainMenuTests.cs b/ILSpy.Tests/MainWindow/MainMenuTests.cs
index 389612aee..3295d850f 100644
--- a/ILSpy.Tests/MainWindow/MainMenuTests.cs
+++ b/ILSpy.Tests/MainWindow/MainMenuTests.cs
@@ -56,6 +56,11 @@ public class MainMenuTests
 	[AvaloniaTest]
 	public async Task Main_Menu_Items_Display_Input_Gestures()
 	{
+		// File → Open carries an InputGestureText="Ctrl+O" attribute on its
+		// [ExportMainMenuCommand]; verifies both the displayed gesture (right side of the menu
+		// item) and the actual HotKey are wired up so Ctrl+O fires from the keyboard too.
+
+		// Arrange — boot MainWindow and wait for the File menu to be populated by MEF.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 
@@ -65,10 +70,12 @@ public class MainMenuTests
 				&& menu.Items.OfType<MenuItem>().Single(m => (string?)m.Tag == nameof(Resources._File))
 					.Items.OfType<MenuItem>().Any());
 
+		// Act — locate the Open MenuItem under File.
 		var fileMenu = menu.Items.OfType<MenuItem>().Single(m => (string?)m.Tag == nameof(Resources._File));
 		var openItem = fileMenu.Items.OfType<MenuItem>()
 			.Single(m => string.Equals(m.Header as string, Resources._Open, System.StringComparison.Ordinal));
 
+		// Assert — both display gesture and hot-key bind to Ctrl+O.
 		openItem.InputGesture.Should().NotBeNull();
 		openItem.InputGesture!.Should().Be(KeyGesture.Parse("Ctrl+O"));
 		openItem.HotKey.Should().Be(KeyGesture.Parse("Ctrl+O"));
diff --git a/ILSpy.Tests/MainWindow/MainWindowTests.cs b/ILSpy.Tests/MainWindow/MainWindowTests.cs
index a507fa254..f934a05a8 100644
--- a/ILSpy.Tests/MainWindow/MainWindowTests.cs
+++ b/ILSpy.Tests/MainWindow/MainWindowTests.cs
@@ -43,9 +43,14 @@ public class MainWindowTests
 	[AvaloniaTest]
 	public void MainWindow_Resolves_From_Composition_And_Shows()
 	{
+		// Smoke-test that MEF resolves MainWindow, the window shows, and its DataContext is the
+		// MainWindowViewModel — the foundation every other UI test relies on.
+
+		// Arrange + Act — resolve and show.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 
+		// Assert — visible, titled, with the correct DataContext.
 		window.IsVisible.Should().BeTrue();
 		window.Title.Should().Be("ILSpy");
 		window.DataContext.Should().BeOfType<MainWindowViewModel>();
@@ -54,12 +59,17 @@ public class MainWindowTests
 	[AvaloniaTest]
 	public async Task Assembly_Tree_Pane_Is_Visible_In_Layout()
 	{
+		// The dock layout must materialise an AssemblyListPane on first show with non-zero
+		// bounds, otherwise the user is staring at a blank window.
+
+		// Arrange + Act — boot the window and wait for the pane to be realized in the visual tree.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 
 		await Waiters.WaitForAsync(() => window.GetVisualDescendants().OfType<AssemblyListPane>().Any());
 		var pane = window.GetVisualDescendants().OfType<AssemblyListPane>().Single();
 
+		// Assert — visible with positive width and height.
 		pane.IsVisible.Should().BeTrue();
 		pane.Bounds.Width.Should().BeGreaterThan(0);
 		pane.Bounds.Height.Should().BeGreaterThan(0);
@@ -68,17 +78,21 @@ public class MainWindowTests
 	[AvaloniaTest]
 	public async Task Toolbar_Disabled_Button_Renders_Dimmed_Icon()
 	{
-		var window = AppComposition.Current.GetExport<MainWindow>();
-		window.Show();
-
 		// At startup the Back button is disabled (no nav history yet — the bound Command's
 		// CanExecute returns false). Its icon should render visibly dimmer so the user can
 		// tell at a glance that it's not clickable.
+
+		// Arrange + Act — show the window, wait until at least one disabled icon-bearing button
+		// has been laid out.
+		var window = AppComposition.Current.GetExport<MainWindow>();
+		window.Show();
+
 		await Waiters.WaitForAsync(() => window.GetVisualDescendants()
 			.OfType<Button>()
 			.Any(b => !b.IsEffectivelyEnabled
 				&& b.GetVisualDescendants().OfType<Image>().Any()));
 
+		// Assert — every disabled toolbar Image must render at <= 0.35 opacity.
 		var dimmedImages = window.GetVisualDescendants()
 			.OfType<Button>()
 			.Where(b => !b.IsEffectivelyEnabled)
@@ -92,6 +106,10 @@ public class MainWindowTests
 	[AvaloniaTest]
 	public async Task Toolbar_Has_Open_Button_Wired_To_Open_Command()
 	{
+		// The MEF-driven Open button (Tag = "Open") must be present in the toolbar with its
+		// Command resolved and enabled.
+
+		// Arrange + Act — show window, wait for the MEF-built Open button to land.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 
@@ -103,6 +121,7 @@ public class MainWindowTests
 			.OfType<Button>()
 			.Single(b => (string?)b.Tag == nameof(ICSharpCode.ILSpy.Properties.Resources.Open));
 
+		// Assert — Command is wired and CanExecute is true.
 		openButton.Command.Should().NotBeNull();
 		openButton.Command!.CanExecute(null).Should().BeTrue();
 	}
@@ -110,6 +129,10 @@ public class MainWindowTests
 	[AvaloniaTest]
 	public async Task Taskbar_Progress_Goes_Indeterminate_While_Decompiling_Then_Clears()
 	{
+		// Selecting a node kicks off a decompile; while it's running the taskbar progress must
+		// transition to Indeterminate, and once done it must drop back to None.
+
+		// Arrange — boot window, wait for assemblies, subscribe to TaskbarProgressService events.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -120,12 +143,14 @@ public class MainWindowTests
 		void Observe(TaskbarProgressState s) => states.Add(s);
 		service.StateChanged += Observe;
 
+		// Act — trigger a decompile.
 		var node = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>("System.Linq");
 		vm.AssemblyTreeModel.SelectedItem = node;
 		await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
 		service.StateChanged -= Observe;
 
+		// Assert — Indeterminate appeared mid-flight and None is the final state.
 		states.Should().Contain(TaskbarProgressState.Indeterminate,
 			"taskbar must show indeterminate progress while a decompile is in flight");
 		states.Last().Should().Be(TaskbarProgressState.None,
diff --git a/ILSpy.Tests/Navigation/NavigationTests.cs b/ILSpy.Tests/Navigation/NavigationTests.cs
index b5c7f7d8b..6c02fe9aa 100644
--- a/ILSpy.Tests/Navigation/NavigationTests.cs
+++ b/ILSpy.Tests/Navigation/NavigationTests.cs
@@ -40,6 +40,12 @@ public class NavigationTests
 	[AvaloniaTest]
 	public async Task Back_Navigation_Restores_Previously_Selected_Node()
 	{
+		// Selecting two methods in succession records both in the navigation history; pressing
+		// the Back command must restore the previously-selected node, re-decompile it, and
+		// scroll the tree so that node is back in view.
+
+		// Arrange — boot the window, wait for assemblies, expand Enumerable, capture two methods
+		// that we'll bounce between.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -47,12 +53,13 @@ public class NavigationTests
 
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var firstMethod = typeNode.Children.OfType<MethodTreeNode>()
 			.Single(m => m.MethodDefinition.Name == "AsEnumerable");
 		var secondMethod = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "Empty");
 
+		// Act 1 — select AsEnumerable, wait for it to decompile.
 		vm.AssemblyTreeModel.SelectedItem = firstMethod;
 		var firstTab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 		firstTab.Text.Should().Contain("AsEnumerable");
@@ -61,14 +68,18 @@ public class NavigationTests
 		// past that window so the second selection records a real back-history entry.
 		await Task.Delay(600);
 
+		// Act 2 — select Empty, wait for its decompile.
 		vm.AssemblyTreeModel.SelectedItem = secondMethod;
 		await Waiters.WaitForAsync(() => ReferenceEquals(vm.AssemblyTreeModel.SelectedItem, secondMethod));
 		var secondTab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 		secondTab.Text.Should().Contain("Empty");
 
+		// Act 3 — fire NavigateBack.
 		vm.DockWorkspace.NavigateBackCommand.CanExecute(null).Should().BeTrue();
 		vm.DockWorkspace.NavigateBackCommand.Execute(null);
 
+		// Assert — selection restores to AsEnumerable, the document re-decompiles to its body,
+		// and the row is centred back into view.
 		await Waiters.WaitForAsync(() => ReferenceEquals(vm.AssemblyTreeModel.SelectedItem, firstMethod));
 		var restoredTab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
 		restoredTab.Text.Should().Contain("AsEnumerable");
@@ -80,6 +91,12 @@ public class NavigationTests
 	[AvaloniaTest]
 	public async Task Back_SplitButton_Dropdown_Lists_History_And_Jumps_To_Selected_Entry()
 	{
+		// The Back button on the toolbar is a SplitButton whose chevron drops a list of recent
+		// history entries. Verifies that the menu populates newest-first from the back stack,
+		// and that picking a non-immediate entry jumps multiple steps in one click (with the
+		// displaced entries pushed onto the forward stack).
+
+		// Arrange — boot, wait for assemblies, expand Enumerable, capture three methods.
 		var window = AppComposition.Current.GetExport<MainWindow>();
 		window.Show();
 		var vm = (MainWindowViewModel)window.DataContext!;
@@ -87,7 +104,7 @@ public class NavigationTests
 
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
-		typeNode.EnsureLazyChildren();
+		typeNode.IsExpanded = true;
 		var methodA = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "AsEnumerable");
 		var methodB = typeNode.Children.OfType<MethodTreeNode>()
@@ -95,8 +112,8 @@ public class NavigationTests
 		var methodC = typeNode.Children.OfType<MethodTreeNode>()
 			.First(m => m.MethodDefinition.Name == "Range");
 
-		// Three distinct selections with >0.6s gaps so each lands as its own entry on the back stack
-		// (NavigationHistory collapses sub-0.5s rapid succession into one entry).
+		// Act 1 — three distinct selections with >0.6s gaps so each lands as its own entry on
+		// the back stack (NavigationHistory collapses sub-0.5s rapid succession into one entry).
 		vm.AssemblyTreeModel.SelectedItem = methodA;
 		await vm.DockWorkspace.WaitForDecompiledTextAsync();
 		await Task.Delay(600);
@@ -106,27 +123,27 @@ public class NavigationTests
 		vm.AssemblyTreeModel.SelectedItem = methodC;
 		await vm.DockWorkspace.WaitForDecompiledTextAsync();
 
-		// Open the Back SplitButton's flyout — the Opening handler populates the menu from the
-		// current back history.
+		// Act 2 — open the Back SplitButton's flyout. The Opening handler populates the menu
+		// from the current back history.
 		var backSplit = window.GetVisualDescendants().OfType<SplitButton>()
 			.Single(sb => sb.Name == "BackSplitButton");
 		var flyout = (MenuFlyout)backSplit.Flyout!;
 		flyout.ShowAt(backSplit);
 		await Waiters.WaitForAsync(() => flyout.Items.OfType<MenuItem>().Count() >= 2);
 
-		// Newest-first: index 0 is the immediate previous selection (methodB),
-		// index 1 is the one before that (methodA).
+		// Assert 1 — newest-first ordering: index 0 is the immediate previous selection
+		// (methodB), index 1 is the one before that (methodA).
 		var items = flyout.Items.OfType<MenuItem>().ToList();
 		((string)items[0].Header!).Should().Be((string)methodB.Text);
 		((string)items[1].Header!).Should().Be((string)methodA.Text);
 		items[1].CommandParameter.Should().BeSameAs(methodA);
 
-		// Multi-step jump: clicking methodA pops two entries off the back stack in one go.
+		// Act 3 — multi-step jump: clicking methodA pops two entries off the back stack in one go.
 		items[1].Command!.Execute(items[1].CommandParameter);
 		await Waiters.WaitForAsync(() => ReferenceEquals(vm.AssemblyTreeModel.SelectedItem, methodA));
 
-		// The two displaced entries (methodC, methodB) are now on the forward stack, so Forward
-		// becomes available.
+		// Assert 2 — the two displaced entries (methodC, methodB) are now on the forward stack,
+		// so Forward becomes available.
 		vm.DockWorkspace.NavigateForwardCommand.CanExecute(null).Should().BeTrue();
 	}
 }
diff --git a/ILSpy.Tests/Resources/IconCompositionTests.cs b/ILSpy.Tests/Resources/IconCompositionTests.cs
index 55df1f3f4..04fd32202 100644
--- a/ILSpy.Tests/Resources/IconCompositionTests.cs
+++ b/ILSpy.Tests/Resources/IconCompositionTests.cs
@@ -32,7 +32,13 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void Public_Method_Has_No_Overlays_And_Full_Sized_Base()
 	{
+		// Public members are the unmarked default — no accessibility overlay glyph and no
+		// shrinkdown; the base image renders 1:1.
+
+		// Arrange + Act — request a Public Method icon.
 		var icon = (LayeredImage)Images.GetIcon(Images.Method, AccessOverlayIcon.Public);
+
+		// Assert — base is the Method bitmap, no overlays, full scale.
 		icon.BaseImage.Should().BeSameAs(Images.Method);
 		icon.Overlays.Should().BeEmpty();
 		icon.BaseScale.Should().Be(1.0);
@@ -41,7 +47,13 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void Private_Method_Composes_Method_Plus_OverlayPrivate_At_80_Percent()
 	{
+		// Adding an accessibility overlay (Private here) shrinks the base to 80% so the overlay
+		// glyph has visual room to sit in the bottom-right corner.
+
+		// Arrange + Act — request a Private Method icon.
 		var icon = (LayeredImage)Images.GetIcon(Images.Method, AccessOverlayIcon.Private);
+
+		// Assert — base shrinks to 0.8, exactly one overlay (the Private padlock).
 		icon.BaseImage.Should().BeSameAs(Images.Method);
 		icon.BaseScale.Should().Be(0.8);
 		icon.Overlays.Should().Equal(Images.OverlayPrivate);
@@ -50,7 +62,13 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void Static_Public_Field_Composes_Field_Plus_OverlayStatic_At_80_Percent()
 	{
+		// `static` adds a Static overlay glyph even when the member is Public — any non-default
+		// modifier triggers the 0.8 base shrink.
+
+		// Arrange + Act — request a static Public Field icon.
 		var icon = (LayeredImage)Images.GetIcon(Images.Field, AccessOverlayIcon.Public, isStatic: true);
+
+		// Assert — base shrinks to 0.8 with just the Static glyph layered on top.
 		icon.BaseImage.Should().BeSameAs(Images.Field);
 		icon.BaseScale.Should().Be(0.8);
 		icon.Overlays.Should().Equal(Images.OverlayStatic);
@@ -59,7 +77,12 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void Extension_Method_Composes_Method_Plus_OverlayExtension_At_80_Percent()
 	{
+		// Extension methods get the dedicated Extension overlay even when the member is Public.
+
+		// Arrange + Act — request a Public extension Method icon.
 		var icon = (LayeredImage)Images.GetIcon(Images.Method, AccessOverlayIcon.Public, isExtension: true);
+
+		// Assert — base shrinks to 0.8 with the Extension glyph as the lone overlay.
 		icon.BaseImage.Should().BeSameAs(Images.Method);
 		icon.BaseScale.Should().Be(0.8);
 		icon.Overlays.Should().Equal(Images.OverlayExtension);
@@ -68,8 +91,14 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void Static_Private_Method_Layers_Static_Then_Private_Over_Method_At_80_Percent()
 	{
-		// Order matches the WPF host's draw sequence: extension → static → accessibility.
+		// Order matters: the layering sequence (extension → static → accessibility) determines
+		// which glyphs end up on top when corners overlap. A static private method must layer
+		// Static under Private so the accessibility glyph remains visible.
+
+		// Arrange + Act — request a static Private Method icon.
 		var icon = (LayeredImage)Images.GetIcon(Images.Method, AccessOverlayIcon.Private, isStatic: true);
+
+		// Assert — overlays are Static followed by Private (back-to-front draw order).
 		icon.BaseImage.Should().BeSameAs(Images.Method);
 		icon.BaseScale.Should().Be(0.8);
 		icon.Overlays.Should().Equal(Images.OverlayStatic, Images.OverlayPrivate);
@@ -78,8 +107,14 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void Static_Extension_Method_Layers_Extension_Then_Static_Then_Internal()
 	{
+		// All three modifiers at once exercises the full layering rule: extension → static →
+		// accessibility, in that draw order.
+
+		// Arrange + Act — request an internal static extension Method icon.
 		var icon = (LayeredImage)Images.GetIcon(Images.Method, AccessOverlayIcon.Internal,
 			isStatic: true, isExtension: true);
+
+		// Assert — three overlays in the documented order.
 		icon.BaseImage.Should().BeSameAs(Images.Method);
 		icon.BaseScale.Should().Be(0.8);
 		icon.Overlays.Should().Equal(Images.OverlayExtension, Images.OverlayStatic, Images.OverlayInternal);
@@ -88,7 +123,13 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void Protected_Event_Composes_Event_Plus_OverlayProtected()
 	{
+		// Sanity-check that the same composition rules apply across base bitmaps (Event here,
+		// not just Method/Field).
+
+		// Arrange + Act — request a Protected Event icon.
 		var icon = (LayeredImage)Images.GetIcon(Images.Event, AccessOverlayIcon.Protected);
+
+		// Assert — base shrinks to 0.8 with the Protected glyph as the lone overlay.
 		icon.BaseImage.Should().BeSameAs(Images.Event);
 		icon.BaseScale.Should().Be(0.8);
 		icon.Overlays.Should().Equal(Images.OverlayProtected);
@@ -97,8 +138,15 @@ public class IconCompositionTests
 	[AvaloniaTest]
 	public void GetIcon_Caches_Same_Composition()
 	{
+		// Decompiling a large assembly produces hundreds of identically-decorated members;
+		// GetIcon must memoise on (base, overlay, isStatic, isExtension) so we don't recreate
+		// the same LayeredImage repeatedly.
+
+		// Arrange + Act — request the same composition twice.
 		var first = Images.GetIcon(Images.Property, AccessOverlayIcon.Internal);
 		var second = Images.GetIcon(Images.Property, AccessOverlayIcon.Internal);
+
+		// Assert — reference equality proves caching.
 		first.Should().BeSameAs(second, "GetIcon must memoise by (base, overlay, isStatic, isExtension)");
 	}
 }
diff --git a/ILSpy.Tests/Resources/ResourceFactoryTests.cs b/ILSpy.Tests/Resources/ResourceFactoryTests.cs
index e33938e7c..cb626d358 100644
--- a/ILSpy.Tests/Resources/ResourceFactoryTests.cs
+++ b/ILSpy.Tests/Resources/ResourceFactoryTests.cs
@@ -63,14 +63,22 @@ public class ResourceFactoryTests
 	[TestCase("strings.resources")]
 	public void Typed_Resource_Names_Route_To_Specialised_Node(string name)
 	{
+		// Each known resource extension (.xsd/.xml/.png/.bmp/.ico/.cur/.resources/...) has a
+		// dedicated ResourceNodeFactory that produces a richer node than the generic
+		// ResourceTreeNode fallback. Verifies the dispatcher picks the typed handler for every
+		// recognised extension regardless of the stream's actual contents.
+
+		// Arrange — boot composition so the static ResourceNodeFactories list is populated; build
+		// a tiny dummy payload (typed-routing must be name-based, not content-based).
 		EnsureComposition();
-		// Tiny payload — node creation must not depend on stream contents being parseable.
 		var payload = Encoding.UTF8.GetBytes("<root />");
+
+		// Act — dispatch the resource through the factory pipeline.
 		var node = ResourceEntryNode.Create(new ByteArrayResource(name, payload));
 
-		// Anything ending in a known extension must NOT fall back to the generic node — the
-		// dispatcher's whole job is to pick the right typed handler. Compare by exact type
-		// (not BeOfType) since SharpTreeNode has a custom .Should() extension in this assembly.
+		// Assert — the produced node is anything *but* the generic fallback. Compare by exact
+		// type (not BeOfType) since SharpTreeNode has a custom .Should() extension in this
+		// assembly that hides BeOfType.
 		node.GetType().Should().NotBe(typeof(ResourceTreeNode),
 			$"resource '{name}' should be routed to a specialised node, not the generic fallback");
 	}
@@ -78,14 +86,30 @@ public class ResourceFactoryTests
 	[AvaloniaTest]
 	public void Unknown_Extension_Falls_Back_To_Generic_Resource_Node()
 	{
+		// Resources whose extension isn't in any factory's claim list must fall back to the
+		// plain ResourceTreeNode (which renders as a hex/text dump) rather than throwing or
+		// silently dropping the entry.
+
+		// Arrange — boot composition; pick an extension nobody handles.
 		EnsureComposition();
+
+		// Act — dispatch the unknown-extension resource.
 		var node = ResourceEntryNode.Create(new ByteArrayResource("data.bin", new byte[] { 1, 2, 3 }));
+
+		// Assert — exactly the generic ResourceTreeNode comes back.
 		node.GetType().Should().Be(typeof(ResourceTreeNode));
 	}
 
 	[AvaloniaTest]
 	public void Resources_File_Decompile_Emits_UIElements_For_String_And_Object_Tables()
 	{
+		// A .resources file should render inline as two DataGrids (one for string entries, one
+		// for non-string objects) sitting alongside the inherited Save button. Drives the
+		// ResourcesFileTreeNode.Decompile implementation that emits AddUIElement calls instead
+		// of plain comment lines.
+
+		// Arrange — boot composition, build a fixture .resources stream with mixed string and
+		// numeric entries, force lazy children, grab the active language for WriteCommentLine.
 		EnsureComposition();
 		var node = (ResourcesFileTreeNode)ResourceEntryNode.Create(
 			new ByteArrayResource("strings.resources", BuildResources(
@@ -97,13 +121,13 @@ public class ResourceFactoryTests
 				})));
 		node.EnsureLazyChildren();
 		var output = new AvaloniaEditTextOutput();
-		// Use the active language so WriteCommentLine works without reaching into MEF state.
 		var language = AppComposition.Current.GetExport<LanguageService>().CurrentLanguage;
+
+		// Act — decompile the resource node into the AvaloniaEdit text output.
 		node.Decompile(language, output, new DecompilationOptions());
 
-		// Two grids (string + object) on top of the inherited Save button = 3 UI elements.
-		// The previous implementation emitted comment lines and only the inherited Save button,
-		// so this drives adding two AddUIElement(...) calls in ResourcesFileTreeNode.Decompile.
+		// Assert — exactly three UI elements (string grid + object grid + inherited Save button)
+		// and they all materialise as Avalonia Controls.
 		output.UIElements.Should().HaveCount(3,
 			".resources should render a string table + object table inline alongside the Save button");
 		var realised = output.UIElements.Select(kv => kv.Value.Value).ToList();
@@ -113,6 +137,12 @@ public class ResourceFactoryTests
 	[AvaloniaTest]
 	public void Resources_File_WriteResX_Round_Trips_String_And_Object_Entries()
 	{
+		// ResourcesFileTreeNode.WriteResX is the format converter behind the "Save as ResX"
+		// option in the resource Save dialog. Verifies it produces well-formed ResX XML with
+		// both string and non-string entries faithfully serialised.
+
+		// Arrange — boot composition; build a fixture .resources stream with one string and one
+		// integer entry; force lazy children so the resource enumeration is realised.
 		EnsureComposition();
 		var node = (ResourcesFileTreeNode)ResourceEntryNode.Create(
 			new ByteArrayResource("strings.resources", BuildResources(
@@ -122,11 +152,12 @@ public class ResourceFactoryTests
 				})));
 		node.EnsureLazyChildren();
 
+		// Act — write the ResX XML into a memory stream and decode it.
 		var ms = new MemoryStream();
 		node.WriteResX(ms);
 		var resx = Encoding.UTF8.GetString(ms.ToArray());
 
-		// ResX is XML; spot-check both entries land with name + value markup.
+		// Assert — both entries land with proper name + value markup (ResX is XML).
 		resx.Should().Contain("<data name=\"greeting\"");
 		resx.Should().Contain("<value>hello</value>");
 		resx.Should().Contain("<data name=\"answer\"");
@@ -136,8 +167,15 @@ public class ResourceFactoryTests
 	[Test]
 	public void FilePickers_ParseFilter_Splits_Pipe_Separated_Display_And_Patterns()
 	{
+		// FilePickers.ParseFilter translates the legacy WPF "Display|*.ext|Display|*.ext"
+		// filter string into Avalonia FilePickerFileType records. Verifies the splitter pairs
+		// up display name with the matching glob pattern correctly.
+
+		// Arrange + Act — feed a two-format filter string through the parser.
 		var types = global::ILSpy.Commands.FilePickers.ParseFilter(
 			"Resources file (*.resources)|*.resources|Resource XML (*.resx)|*.resx");
+
+		// Assert — two file types come back, each with the right display name and pattern.
 		types.Should().HaveCount(2);
 		types[0].Name.Should().Be("Resources file (*.resources)");
 		types[0].Patterns.Should().BeEquivalentTo(new[] { "*.resources" });