anchor.diff:          options: options, showDiagnostics: verbose);
       FormattingDiagnosticHandler diagnostics =
           new FormattingDiagnosticHandler(compiler.provider);
  -    HelperAnalyzer analyzer = new HelperAnalyzer(diagnostics);
       Directory dir =
           new Directory.fromUri(Uri.base.resolve('pkg/compiler/lib/'));
  +    String helpersUriPrefix = dir.uri.resolve('src/helpers/').toString();
  +    HelperAnalyzer analyzer = new HelperAnalyzer(diagnostics, helpersUriPrefix);
  +    LibraryElement helperLibrary;
       for (FileSystemEntity entity in dir.listSync(recursive: true)) {
         if (entity is File && entity.path.endsWith('.dart')) {
           Uri file = Uri.base.resolve(nativeToUriPath(entity.path));
  
positive.code: 
    AnalyzableElement get analyzedElement => resolvedAst.element;
  
    HelperAnalyzer(this.diagnostics) : super(null);
  
    @override
    void apply(Node node, [_]) {
  
negative.code:         }
        }
      }
      Expect.isNotNull(helperLibrary, 'Helper library not found');
      Expect.isTrue(analyzer.isHelper(helperLibrary),
          "Helper library $helperLibrary is not considered a helper.");
      Expect.isTrue(analyzer.errors.isEmpty, "Errors found.");
    });
  }
  
  class HelperAnalyzer extends TraversalVisitor {
    final FormattingDiagnosticHandler diagnostics;
    final String helpersUriPrefix;
    List<SourceSpan> errors = <SourceSpan>[];
  
    ResolvedAst resolvedAst;
  