code: def gen_internal_address(
      cls, process_index: int, external_address: str = None
  ) -> str:
      return f"dummy://{process_index}"
  
file_path: mars/mars/oscar/backends/test/pool.py
imports: import asyncio
  import multiprocessing
  from typing import List, Dict
  from ..config import ActorPoolConfig
  from ..communication import gen_local_address, DummyServer
  from ..mars.pool import MainActorPool, SubActorPool, SubpoolStatus
  from ..pool import ActorPoolType
label_desc: Use image node_id 2 for calling the TestMainActorPool obj's underlying member method code with example usage: obj.gen_internal_address(cls, process_index, external_address) and returns: str, process_index