anchor.diff:  
   final _formatter = new dart_style.DartFormatter();
   
  -Future<CompilationUnit> _getCompilationUnitForString(String projectPath) async {
  -  var fileName = 'json_serializable_test_input.dart';
  -  var filePath = p.join(getPackagePath(), 'test', 'src', fileName);
  -  var source =
  -      new StringSource(new File(filePath).readAsStringSync(), fileName);
  -
  -  var context = await getAnalysisContextForProjectPath(projectPath);
  -
  +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);
   }
  
positive.code: 
  void main() {
    setUpAll(() async {
      _compUnit = await _getCompilationUnitForString(getPackagePath());
    });
  
    group('without wrappers',
  
negative.code: // TODO(kevmoo): test all flavors of `nullable` - class, fields, etc
  
  import 'dart:async';
  
  import 'package:analyzer/dart/ast/ast.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';
  