code: def redis_replicas(monkeypatch):
      monkeypatch.setenv("TEST_EXTERNAL_REDIS_REPLICAS", "3")
  
imports: import sys
  import os
  import threading
  from time import sleep
  import pytest
  import ray
  from ray._private.utils import get_or_create_event_loop
  from ray.util.scheduling_strategies import PlacementGroupSchedulingStrategy
  import ray._private.gcs_utils
  from ray._private import ray_constants
  from ray._private.test_utils import convert_actor_state, enable_external_redis, generate_system_config_map, wait_for_condition, wait_for_pid_to_exit, run_string_as_driver
  from ray.job_submission import JobSubmissionClient, JobStatus
  from ray._raylet import GcsClient
  import psutil
label_desc: Use image node_id 18 for calling a global function with example usage: redis_replicas(monkeypatch) without return types