input: Write a python function to log errors to a file named 'app_error.log' using the logging module.
  assert 'app_error.log' in [handler.baseFilename for handler in logging.getLogger('logutil').handlers if isinstance(handler, logging.FileHandler)]
  assert logging.getLogger('logutil').level == logging.ERROR
output: import logging
  
  def setup_error_logger():
      logger = logging.getLogger('logutil')
      logger.setLevel(logging.ERROR)
      
      # Create file handler which logs error messages
      fh = logging.FileHandler('app_error.log')
      fh.setLevel(logging.ERROR)
      
      # Create formatter and add it to the handlers
      formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
      fh.setFormatter(formatter)
      
      # Add the handlers to the logger
      logger.addHandler(fh)
      
      return logger
  
  # Initialize the logger
  error_logger = setup_error_logger()