[duplicate-code] Duplicate Code: Scaffolding Pattern in StringAssertToAssertFixer and CollectionAssertToAssertFixer

[Evangelink]

Analysis of commit e5fea75 — triggered by @Evangelink

Assignee: @copilot

Summary

CollectionAssertToAssertFixer (added in commit 7a3558e) duplicates the RegisterCodeFixesAsync scaffolding and fix-method skeleton of the pre-existing StringAssertToAssertFixer. The two fixers share four structural patterns — GetFixAllProvider, the diagnostic-property extraction guard, the node-finding guard, and the document-root rewrite pattern — totalling ~22 near-identical lines before the argument-rewriting logic diverges.

Duplication Details

Pattern 1 — Identical GetFixAllProvider (2 lines)

• Severity: Low
• Occurrences: 2 identical implementations
• Locations:
  • src/Analyzers/MSTest.Analyzers.CodeFixes/StringAssertToAssertFixer.cs
  • src/Analyzers/MSTest.Analyzers.CodeFixes/CollectionAssertToAssertFixer.cs
• Code Sample:

  public sealed override FixAllProvider GetFixAllProvider()
      => WellKnownFixAllProviders.BatchFixer;

Pattern 2 — Near-identical RegisterCodeFixesAsync scaffolding (~18 lines)

• Severity: High
• Occurrences: 2
• Locations:
  • src/Analyzers/MSTest.Analyzers.CodeFixes/StringAssertToAssertFixer.cs (RegisterCodeFixesAsync)
  • src/Analyzers/MSTest.Analyzers.CodeFixes/CollectionAssertToAssertFixer.cs (RegisterCodeFixesAsync)
• Code Sample:

  // Both fixers follow this identical scaffold (only the resource key and
  // analyzer class name differ):
  SyntaxNode root = await context.Document
      .GetRequiredSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
  Diagnostic diagnostic = context.Diagnostics[0];
  if (!diagnostic.Properties.TryGetValue(XxxAnalyzer.ProperAssertMethodNameKey,
          out string? properAssertMethodName)
      || properAssertMethodName == null)
  {
      return;
  }
  if (root.FindNode(diagnostic.Location.SourceSpan, getInnermostNodeForTie: true)
          is not InvocationExpressionSyntax invocationExpr)
  {
      return;
  }
  if (invocationExpr.Expression is not MemberAccessExpressionSyntax)
  {
      return;
  }
  string title = string.Format(CultureInfo.InvariantCulture, CodeFixResources.XxxTitle, properAssertMethodName);
  var action = CodeAction.Create(
      title: title,
      createChangedDocument: ct => FixXxxAsync(context.Document, invocationExpr, ..., ct),
      equivalenceKey: title);
  context.RegisterCodeFix(action, diagnostic);

Pattern 3 — Near-identical fix method skeleton (~6 lines)

• Severity: Medium
• Occurrences: 2
• Locations:
  • src/Analyzers/MSTest.Analyzers.CodeFixes/StringAssertToAssertFixer.cs (FixStringAssertAsync)
  • src/Analyzers/MSTest.Analyzers.CodeFixes/CollectionAssertToAssertFixer.cs (FixCollectionAssertAsync)
• Code Sample:

  // Both fix methods open with the same guard + root fetch, and close identically:
  if (invocationExpr.Expression is not MemberAccessExpressionSyntax memberAccessExpr)
  {
      return document;
  }
  SyntaxNode root = await document
      .GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
  // ... argument rewriting differs ...
  return document.WithSyntaxRoot(root.ReplaceNode(invocationExpr, newInvocationExpr));

Impact Analysis

• Maintainability: Adding a new XxxAssertToAssertFixer in the future will copy-paste the same scaffolding a third time.
• Bug Risk: A fix to the RegisterCodeFixesAsync guard logic (e.g., handling is null vs == null, or changing how the fix-all scope works) must be applied to multiple fixers manually.
• Code Bloat: ~22 lines of scaffolding duplicated per fixer pair; will grow linearly with future *AssertToAssert rules.

Refactoring Recommendations

1. Shared base class AssertToAssertFixerBase : CodeFixProvider

   • Implement GetFixAllProvider and the common RegisterCodeFixesAsync scaffold (property extraction, node finding, MemberAccessExpressionSyntax guard, CodeAction.Create) in the base.
   • Subclasses override a single abstract method BuildFixedDocumentAsync(Document, InvocationExpressionSyntax, string assertMethodName, string fixKind, CancellationToken) for the argument-rewriting logic.
   • Estimated effort: 2–3 hours.
   • Benefits: single place for the scaffold; future fixers are ~20 lines instead of ~80.

2. Alternative: shared static helper AssertToAssertFixerHelper

   • If inheritance is undesirable (e.g. to keep sealed), extract a static helper with the common guard steps as a TryExtractFixInfo method that both fixers call.
   • Estimated effort: 1–2 hours.

Implementation Checklist

• Review duplication findings
• Choose between base-class and static-helper approach
• Create the shared infrastructure in src/Analyzers/MSTest.Analyzers.CodeFixes/
• Refactor StringAssertToAssertFixer to use it
• Refactor CollectionAssertToAssertFixer to use it
• Verify all existing fixer unit tests still pass
• Run unit tests: MSTest.Analyzers.UnitTests

Analysis Metadata

• Analyzed Files: 2 source files
• Detection Method: Semantic code analysis — structural comparison of recently-added code fixer
• Commit: 7a3558e (Add MSTEST0068)
• Analysis Date: 2026-06-05

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• expires on Jun 7, 2026, 5:55 AM UTC