anchor.diff:    final Match match = pattern.firstMatch(subshardName);
     if (match == null || match.groupCount != 2) {
       print('${red}Invalid subshard name "$subshardName". Expected format "[int]_[int]" ex. "1_3"');
  -    // TODO(jmagman): exit(1) here instead once LUCI configs are migrated to d+_d+ subshard format.
  -    return null;
  +    exit(1);
     }
     // One-indexed.
     final int index = int.parse(match.group(1));
  
positive.code: 
  final bool useFlutterTestFormatter = Platform.environment['FLUTTER_TEST_FORMATTER'] == 'true';
  
  
  /// The number of Cirrus jobs that run build tests in parallel.
  ///
  /// WARNING: if you change this number, also change .cirrus.yml
  /// and make sure it runs _all_ shards.
  const int kBuildTestShardCount = 2;
  
  const String kShardKey = 'SHARD';
  const String kSubshardKey = 'SUBSHARD';
  
  
negative.code:       ],
    ]..shuffle(math.Random(0));
  
    await _runShardRunnerIndexOfTotalSubshard(tests);
  }
  
  Future<void> _runExampleProjectBuildTests(FileSystemEntity exampleDirectory) async {
  