anchor.diff:  /// Creates a package using [pkgName] an the current [d.defaultRoot].
   Future<String> _createPackageStub(String pkgName) async {
     await d
  -      .dir(pkgName, [d.dir('lib', [d.file('person.dart', _personContent)])])
  +      .dir(pkgName, [d.dir('lib', [d.file('person.dart', _testLibContent)])])
         .create();
   
     var pkgPath = p.join(d.defaultRoot, pkgName);
  
positive.code: import 'dart:async';
  import 'dart:io';
  
  import 'package:scheduled_test/descriptor.dart' as d;
  import 'package:scheduled_test/scheduled_test.dart';
  import 'package:path/path.dart' as p;
  
  import 'package:source_gen/src/build_file_generator.dart';
  import 'package:source_gen/json_serial/json_generator.dart';
  
  import 'test_utils.dart';
  
  void main() {
    test('Simple test of JsonGenerator', () {
      String projectPath;
  
      schedule(() async {
  
negative.code:     schedule(() async {
        var filePath = p.join(projectPath, 'lib', 'person.dart');
        var output =
            await generate(getPackagePath(), filePath, [const _TestGenerator()]);
  
        expect(output, isNotNull);
        expect(output, isNotEmpty);
  