code: func (ln *InmemoryListener) Close() error {
  	var err error
  
  	ln.lock.Lock()
  	if !ln.closed {
  		close(ln.conns)
  		ln.closed = true
  	} else {
  		err = fmt.Errorf("InmemoryListener is already closed")
  	}
  	ln.lock.Unlock()
  	return err
  }
docs: // Close implements net.Listener's Close.