Walk the step tree with the helper the repo already has

Three copies of the same pre-order walk across two test files become
TreeTraversal.PreOrder, and the stepper fixture builds its decompiler through
the file-name constructor instead of assembling the type system by hand.

Assisted-by: Claude:claude-opus-5[1m]:Claude Code

ICSharpCode.Decompiler.Tests/DebugStepRecordingTests.cs

@@ -23,6 +23,7 @@ using System.Linq;
 using ICSharpCode.Decompiler.CSharp;
 using ICSharpCode.Decompiler.DebugSteps;
 using ICSharpCode.Decompiler.IL;
+using ICSharpCode.Decompiler.Util;
 using ICSharpCode.Decompiler.IL.Transforms;
 using ICSharpCode.Decompiler.Metadata;
 using ICSharpCode.Decompiler.Tests.Helpers;
@@ -56,7 +57,7 @@ namespace ICSharpCode.Decompiler.Tests
 
 			decompiler.DecompileTypeAsString(SampleType);
 
-			Assert.That(Descriptions(decompiler.Stepper.Steps), Has.Some.Contains(RecordedStep));
+			Assert.That(TreeTraversal.PreOrder(decompiler.Stepper.Steps, n => n.Children).Select(n => n.Description), Has.Some.Contains(RecordedStep));
 		}
 
 		/// <summary>
@@ -72,7 +73,7 @@ namespace ICSharpCode.Decompiler.Tests
 
 			decompiler.DecompileTypeAsString(SampleType);
 
-			Assert.That(Descriptions(decompiler.Stepper.Steps), Has.None.Contains(RecordedStep));
+			Assert.That(TreeTraversal.PreOrder(decompiler.Stepper.Steps, n => n.Children).Select(n => n.Description), Has.None.Contains(RecordedStep));
 		}
 
 		/// <summary>
@@ -301,7 +302,7 @@ namespace ICSharpCode.Decompiler.Tests
 			var decompiler = CreateRecordingDecompiler();
 			decompiler.ILTransforms.Add(detachedStep);
 			decompiler.DecompileTypeAsString(SampleType);
-			int haltAt = AllNodes(decompiler.Stepper.Steps).Single(n => n.Description.Contains(DetachedStep)).BeginStep;
+			int haltAt = TreeTraversal.PreOrder(decompiler.Stepper.Steps, n => n.Children).Single(n => n.Description.Contains(DetachedStep)).BeginStep;
 
 			var replay = CreateRecordingDecompiler();
 			var replayStep = new DetachedFunctionILTransform("CleanUpFileName");
@@ -321,26 +322,6 @@ namespace ICSharpCode.Decompiler.Tests
 			return decompiler.Stepper.Steps.Single(n => n.Description.EndsWith("." + methodName, StringComparison.Ordinal));
 		}
 
-		static IEnumerable<Stepper.Node> AllNodes(IEnumerable<Stepper.Node> nodes)
-		{
-			foreach (var node in nodes)
-			{
-				yield return node;
-				foreach (var child in AllNodes(node.Children))
-					yield return child;
-			}
-		}
-
-		static IEnumerable<string> Descriptions(IEnumerable<Stepper.Node> nodes)
-		{
-			foreach (var node in nodes)
-			{
-				yield return node.Description;
-				foreach (var description in Descriptions(node.Children))
-					yield return description;
-			}
-		}
-
 		static CSharpDecompiler CreateRecordingDecompiler()
 		{
 			var decompiler = StepperTesting.CreateDecompiler();

ICSharpCode.Decompiler.Tests/Helpers/StepperTesting.cs

@@ -37,10 +37,8 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 
 		public static CSharpDecompiler CreateDecompiler()
 		{
-			var module = new PEFile("ICSharpCode.Decompiler.dll");
-			var settings = new DecompilerSettings();
-			var typeSystem = new DecompilerTypeSystem(module, new UniversalAssemblyResolver(null, false, null), settings);
-			return new CSharpDecompiler(typeSystem, settings);
+			return new CSharpDecompiler("ICSharpCode.Decompiler.dll",
+				new UniversalAssemblyResolver(null, false, null), new DecompilerSettings());
 		}
 
 		/// <summary>

ILSpy.Tests/Views/DebugStepsTests.cs

@@ -223,21 +223,10 @@ public class DebugStepsTests
 		var ilTransformNames = CSharpDecompiler.GetILTransforms()
 			.Select(transform => transform.GetType().Name)
 			.ToHashSet();
-		AllDescriptions(csharp.Stepper.Steps).Should().NotContain(
+		ICSharpCode.Decompiler.Util.TreeTraversal.PreOrder(csharp.Stepper.Steps, n => n.Children).Select(n => n.Description).Should().NotContain(
 			description => ilTransformNames.Contains(StripStepNumber(description)),
 			"a closed pane leaves the IL transforms unrecorded");
 		csharp.Stepper.Steps.Should().BeEmpty("a closed pane leaves the whole pipeline unrecorded");
-
-		static System.Collections.Generic.IEnumerable<string> AllDescriptions(
-			System.Collections.Generic.IEnumerable<Stepper.Node> nodes)
-		{
-			foreach (var node in nodes)
-			{
-				yield return node.Description;
-				foreach (var description in AllDescriptions(node.Children))
-					yield return description;
-			}
-		}
 	}
 
 	[AvaloniaTest]