code: def test_checkpoint_isolation_namespace(ray_shutdown):
      info = ray.init(namespace="test_namespace1")
  
      address = info["address"]
  
      driver_template = """
  import ray
  from ray import serve
  
  ray.init(address="{address}", namespace="{namespace}")
  
  serve.start(http_options={{"port": {port}}})
  
  @serve.deployment
  class A:
      pass
  
  serve.run(A.bind())"""
  
      run_string_as_driver(
          driver_template.format(
              address=address, namespace="test_namespace1", port=8000
          )
      )
      run_string_as_driver(
          driver_template.format(
              address=address, namespace="test_namespace2", port=8001
          )
      )
  
imports: import logging
  import os
  import socket
  import sys
  import time
  import pytest
  import requests
  import ray
  import ray._private.gcs_utils
  from ray import serve
  from ray._private.services import new_port
  from ray._private.test_utils import convert_actor_state, run_string_as_driver, wait_for_condition
  from ray._raylet import GcsClient
  from ray.cluster_utils import Cluster, cluster_not_supported
  from ray.serve._private import api
  from ray.serve._private.constants import SERVE_CONTROLLER_NAME, SERVE_DEFAULT_APP_NAME, SERVE_NAMESPACE, SERVE_PROXY_NAME, SERVE_ROOT_URL_ENV_KEY
  from ray.serve._private.default_impl import create_cluster_node_info_cache
  from ray.serve._private.http_util import set_socket_reuse_port
  from ray.serve._private.utils import block_until_http_ready, format_actor_name
  from ray.serve.config import DeploymentMode, HTTPOptions, ProxyLocation
  from ray.serve.context import _get_global_client
  from ray.serve.exceptions import RayServeException
  from ray.serve.schema import ServeApplicationSchema, ServeDeploySchema
  from ray.tests.conftest import maybe_external_redis
  from ray.tests.conftest import ray_start_with_dashboard
  from ray.util.state import list_actors
label_desc: Use image node_id 19 for calling a global function with example usage: test_checkpoint_isolation_namespace(ray_shutdown) without return types