anchor.diff:    });
   
     test('unannotated classes no-op', () {
  -    var element = _getClassForCodeString(_classNoFieldsContent, 'NoAnnotation');
  +    var element = _getClassForCodeString('NoAnnotation');
       var output = _generator.generate(element);
   
       expect(output, isNull);
  
positive.code: 
    group('valid inputs', () {
      test('class with no fields', () {
        var element = _getClassForCodeString(_classNoFieldsContent, 'Person');
        var output = _generator.generate(element);
  
        expect(output, isNotNull);
  
negative.code:   return context.resolveCompilationUnit(source, libElement);
  }
  
  CompilationUnit _compUnit;
  
  const _testSource = r'''
  import 'package:source_gen/json_serial/json_annotation.dart';
  
  @JsonSerializable()
  