code: func (eg *EngineGroup) Ping() error {
  	if err := eg.Engine.Ping(); err != nil {
  		return err
  	}
  
  	for _, slave := range eg.slaves {
  		if err := slave.Ping(); err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // Ping tests if database is alive