code: func ListenOnLocalRandomPort() (net.Listener, error) {
  	ip, err := Localhost()
  	if err != nil {
  		return nil, err
  	}
  	return net.ListenTCP("tcp", &net.TCPAddr{IP: ip, Port: 0})
  }
docs: // ListenOnLocalRandomPort returns a TCP listener on a random
  // localhost port.