anchor.diff:  // TODO(kevmoo): test all flavors of `nullable` - class, fields, etc
   
   import 'dart:async';
  -import 'dart:io';
   
   import 'package:analyzer/dart/ast/ast.dart';
  -import 'package:analyzer/src/string_source.dart';
   import 'package:dart_style/dart_style.dart' as dart_style;
   import 'package:json_serializable/json_serializable.dart';
   import 'package:json_serializable/src/constants.dart';
  
positive.code: 
  void main() {
    setUpAll(() async {
      _compUnit = await _getCompilationUnitForString(getPackagePath());
    });
  
    group('without wrappers',
  
negative.code: 
  final _formatter = new dart_style.DartFormatter();
  
  Future<CompilationUnit> _getCompilationUnitForString() async {
    var context = await getAnalysisContextForProjectPath(getPackagePath());
  
    var fileUri = p.toUri(p.join(
        getPackagePath(), 'test', 'src', 'json_serializable_test_input.dart'));
    var source = context.sourceFactory.forUri2(fileUri);
    var libElement = context.computeLibraryElement(source);
    return context.resolveCompilationUnit(source, libElement);
  }
  