Open-assembly + back-nav tests, fold into one fixture

Added two new headless tests in MainWindowTests:
- Back_Navigation_Restores_Previously_Selected_Node — selects two methods on
  Enumerable, executes DockWorkspace.NavigateBackCommand, asserts the original
  node is reselected, decompiled text reverts, and the row is centred.
- Opening_Assembly_Adds_It_To_The_Tree — drives the production OpenCommand via
  MainMenuCommandRegistry (matched by Resources._Open header), confirms the
  new LoadedAssembly appears, the AssemblyTreeNode is reachable by short name,
  and SharpTreeNode.IsSelected is set on the freshly opened node.

Assisted-by: Claude:claude-opus-4-7:Claude Code

ILSpy.Tests/DecompileAsEnumerableTest.cs

@@ -1,76 +0,0 @@
-// Copyright (c) 2026 AlphaSierraPapa for the SharpDevelop Team
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy of this
-// software and associated documentation files (the "Software"), to deal in the Software
-// without restriction, including without limitation the rights to use, copy, modify, merge,
-// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
-// to whom the Software is furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all copies or
-// substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
-// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
-// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
-// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
-// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-// DEALINGS IN THE SOFTWARE.
-
-using System.Linq;
-using System.Threading.Tasks;
-
-using AwesomeAssertions;
-
-using Avalonia.Headless.NUnit;
-
-using global::ILSpy.AppEnv;
-using global::ILSpy.TreeNodes;
-using global::ILSpy.ViewModels;
-using global::ILSpy.Views;
-
-using NUnit.Framework;
-
-namespace ICSharpCode.ILSpy.Tests;
-
-[TestFixture]
-public class DecompileAsEnumerableTest
-{
-	[AvaloniaTest]
-	public async Task Selecting_AsEnumerable_Method_Decompiles_Into_Document_View()
-	{
-		var window = AppComposition.Current.GetExport<MainWindow>();
-		window.Show();
-		var vm = (MainWindowViewModel)window.DataContext!;
-
-		// MainWindow.Opened triggers AssemblyTreeModel.Initialize, which queues the default
-		// assembly list (System.Private.CoreLib, System, System.Linq) for async loading.
-		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
-
-		// Walk via the production FindNodeByPath (used by SessionSettings.ActiveTreeViewPath
-		// save/restore) down to the type. First segment is the assembly short name; the helper
-		// substitutes the file path AssemblyTreeNode.ToString returns.
-		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
-			"System.Linq", "System.Linq", "System.Linq.Enumerable");
-
-		// Method-level stable identities are built via ILAmbience and impractical to author by
-		// hand, so we expand the type and pick the overload by name. Enumerable has only one
-		// AsEnumerable, so this is unambiguous.
-		typeNode.EnsureLazyChildren();
-		var methodNode = typeNode.Children.OfType<MethodTreeNode>()
-			.Single(m => m.MethodDefinition.Name == "AsEnumerable");
-		methodNode.MethodDefinition.IsExtensionMethod.Should().BeTrue();
-
-		// Selecting the node routes through DockWorkspace -> the active decompiler tab.
-		vm.AssemblyTreeModel.SelectedItem = methodNode;
-
-		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
-		tab.Text.Should().Contain("AsEnumerable");
-		tab.Text.Should().Contain("IEnumerable<TSource>");
-		tab.Text.Should().Contain("return source");
-
-		// Selecting a deeply-nested node must scroll the assembly tree so it's centered.
-		methodNode.Should().Be().CenteredInView();
-
-		window.CaptureAndShow();
-	}
-}

ILSpy.Tests/MainWindow/MainWindowTests.cs

@@ -16,13 +16,20 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System.Linq;
+using System.Threading.Tasks;
+
 using Avalonia.Headless.NUnit;
 
 using AwesomeAssertions;
 
-using global::ILSpy.AppEnv;
-using global::ILSpy.ViewModels;
-using global::ILSpy.Views;
+using ICSharpCode.ILSpy.Properties;
+
+using ILSpy.AppEnv;
+using ILSpy.Commands;
+using ILSpy.TreeNodes;
+using ILSpy.ViewModels;
+using ILSpy.Views;
 
 using NUnit.Framework;
 
@@ -40,7 +47,96 @@ public class MainWindowTests
 		window.IsVisible.Should().BeTrue();
 		window.Title.Should().Be("ILSpy");
 		window.DataContext.Should().BeOfType<MainWindowViewModel>();
+	}
+
+	[AvaloniaTest]
+	public async Task Selecting_AsEnumerable_Method_Decompiles_Into_Document_View()
+	{
+		var window = AppComposition.Current.GetExport<MainWindow>();
+		window.Show();
+		var vm = (MainWindowViewModel)window.DataContext!;
+		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
+
+		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Linq", "System.Linq", "System.Linq.Enumerable");
+		typeNode.EnsureLazyChildren();
+		var methodNode = typeNode.Children.OfType<MethodTreeNode>()
+			.Single(m => m.MethodDefinition.Name == "AsEnumerable");
+		methodNode.MethodDefinition.IsExtensionMethod.Should().BeTrue();
+
+		vm.AssemblyTreeModel.SelectedItem = methodNode;
+		var tab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+		tab.Text.Should().Contain("AsEnumerable");
+		tab.Text.Should().Contain("IEnumerable<TSource>");
+		tab.Text.Should().Contain("return source");
+
+		methodNode.Should().Be().CenteredInView();
+	}
+
+	[AvaloniaTest]
+	public async Task Back_Navigation_Restores_Previously_Selected_Node()
+	{
+		var window = AppComposition.Current.GetExport<MainWindow>();
+		window.Show();
+		var vm = (MainWindowViewModel)window.DataContext!;
+		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
+
+		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Linq", "System.Linq", "System.Linq.Enumerable");
+		typeNode.EnsureLazyChildren();
+		var firstMethod = typeNode.Children.OfType<MethodTreeNode>()
+			.Single(m => m.MethodDefinition.Name == "AsEnumerable");
+		var secondMethod = typeNode.Children.OfType<MethodTreeNode>()
+			.First(m => m.MethodDefinition.Name == "Empty");
+
+		vm.AssemblyTreeModel.SelectedItem = firstMethod;
+		var firstTab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+		firstTab.Text.Should().Contain("AsEnumerable");
+
+		vm.AssemblyTreeModel.SelectedItem = secondMethod;
+		await Waiters.WaitForAsync(() => ReferenceEquals(vm.AssemblyTreeModel.SelectedItem, secondMethod));
+		var secondTab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+		secondTab.Text.Should().Contain("Empty");
+
+		vm.DockWorkspace.NavigateBackCommand.CanExecute(null).Should().BeTrue();
+		vm.DockWorkspace.NavigateBackCommand.Execute(null);
+
+		await Waiters.WaitForAsync(() => ReferenceEquals(vm.AssemblyTreeModel.SelectedItem, firstMethod));
+		var restoredTab = await vm.DockWorkspace.WaitForDecompiledTextAsync();
+		restoredTab.Text.Should().Contain("AsEnumerable");
+		restoredTab.Text.Should().Contain("return source");
+
+		firstMethod.Should().Be().CenteredInView();
+	}
+
+	[AvaloniaTest]
+	public async Task Opening_Assembly_Adds_It_To_The_Tree()
+	{
+		var window = AppComposition.Current.GetExport<MainWindow>();
+		window.Show();
+		var vm = (MainWindowViewModel)window.DataContext!;
+		await vm.AssemblyTreeModel.WaitForAssembliesAsync(minimumCount: 3);
+
+		var newAsmPath = typeof(System.Net.Http.HttpClient).Assembly.Location;
+		var initialCount = vm.AssemblyTreeModel.AssemblyList!.Count;
+
+		var registry = AppComposition.Current.GetExport<MainMenuCommandRegistry>();
+		var openCommand = registry.Commands
+			.Single(c => c.Metadata.Header == nameof(Resources._Open))
+			.CreateExport().Value;
+		openCommand.Execute(newAsmPath);
+
+		await Waiters.WaitForAsync(() =>
+			vm.AssemblyTreeModel.AssemblyList!.GetAssemblies().Any(a =>
+				string.Equals(a.FileName, newAsmPath, System.StringComparison.OrdinalIgnoreCase)));
+
+		var loaded = vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
+			.First(a => string.Equals(a.FileName, newAsmPath, System.StringComparison.OrdinalIgnoreCase));
+		await loaded.GetLoadResultAsync();
 
-		window.CaptureAndShow();
+		vm.AssemblyTreeModel.AssemblyList!.Count.Should().Be(initialCount + 1);
+		var node = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(loaded.ShortName);
+		node.LoadedAssembly.Should().BeSameAs(loaded);
+		node.IsSelected.Should().BeTrue();
 	}
 }

ILSpy.Tests/TestApp.axaml.cs

@@ -23,7 +23,7 @@ using ICSharpCode.ILSpyX.Settings;
 
 using ILSpy.AppEnv;
 
-using ProductionApp = global::ILSpy.App;
+using ProductionApp = ILSpy.App;
 
 namespace ICSharpCode.ILSpy.Tests;