anchor.diff:    if (!_initialized) {
       print('unittest-suite-wait-for-done');
       _initialized = true;
  -    _port = new ReceivePort();
     }
     _asyncLevel += count;
   }
  
positive.code:   }
    _asyncLevel--;
    if (_asyncLevel == 0) {
      _port.close();
      _port = null;
      print('unittest-suite-success');
    }
  }
  
negative.code: 
  library async_helper;
  
  bool _initialized = false;
  int _asyncLevel = 0;
  
  Exception _buildException(String msg) {
  