code: def add(self, a, b):
      return a + b + c
  
imports: import unittest
  from parl.utils import logger
  import parl
  from parl.remote.client import disconnect
  from parl.remote.master import Master
  from parl.utils import get_free_tcp_port
  from parl.remote.worker import Worker
  from parl.utils.test_utils import XparlTestCase
  import time
  import threading
  import os
  import signal
  import subprocess
label_desc: Use image node_id 1 for calling the Actor obj's underlying member method code with example usage: obj.add(a, b) and returns: unknown