docs: def progress_callback(self, action, node, elapsed_time=None):
          """
          Callback to report progress
  
          :param str action:
          :param list node: app, module
          :param int | None elapsed_time:
          """
          if action == 'load_start':
              self.stdout.write('Loading fixture {}.{}...'.format(*node),
                                ending='')
              self.stdout.flush()
          elif action == 'load_success':
              message = 'SUCCESS'
              if elapsed_time:
                  message += ' ({:.03} seconds) '.format(elapsed_time)
  
              self.stdout.write(message)