docs: def _validate_type(self, file_name, extension_map, method_title, argument_title):
  
          ''' a helper method to validate extension type of file
  
          :param file_name: string with file name to test
          :param extension_map: dictionary with extensions names and regex patterns
          :param method_title: string with title of feeder method
          :param argument_title: string with title of argument key from feeder method
          :return: string with file extension
          '''
  
      # validate file extension
          from labpack.parsing.regex import labRegex
          file_extension = ''
          ext_types = labRegex(extension_map)
          file_mapping = ext_types.map(file_name)[0]
          extension_list = []
          for key, value in file_mapping.items():
              if isinstance(value, bool):
                  extension_list.append('.%s' % key)
              if value and isinstance(value, bool):
                  file_extension = '.%s' + key
          if not file_extension:
              raise ValueError('%s(%s=%s) must be one of %s file types.' % (method_title, argument_title, file_name, extension_list))
  
          return file_extension