code: def test_namespace(ray_start_cluster):
      """
      Most of the "checks" in this test case rely on the fact that
      `run_string_as_driver` will throw an exception if the driver string exits
      with a non-zero exit code (e.g. when the driver scripts throws an
      exception). Since all of these drivers start named, detached actors, the
      most likely failure case would be a collision of named actors if they're
      put in the same namespace.
  
      This test checks that:
      * When two drivers don't specify a namespace, they are placed in different
        anonymous namespaces.
      * When two drivers specify a namespace, they collide.
      * The namespace name (as provided by the runtime context) is correct.
      """
      cluster = ray_start_cluster
      cluster.add_node(num_cpus=4, ray_client_server_port=50055)
      cluster.wait_for_nodes(1)
  
      template = """
  import ray
  ray.client("localhost:50055").namespace({namespace}).connect()
  
  @ray.remote
  class Foo:
      def ping(self):
          return "pong"
  
  a = Foo.options(lifetime="detached", name="abc").remote()
  ray.get(a.ping.remote())
  print("Current namespace:", ray.get_runtime_context().namespace)
      """
  
      anon_driver = template.format(namespace="None")
      run_string_as_driver(anon_driver)
      # This second run will fail if the actors don't run in separate anonymous
      # namespaces.
      run_string_as_driver(anon_driver)
  
      run_in_namespace = template.format(namespace="'namespace'")
      script_output = run_string_as_driver(run_in_namespace)
      # The second run fails because the actors are run in the same namespace.
      with pytest.raises(subprocess.CalledProcessError):
          run_string_as_driver(run_in_namespace)
  
      assert "Current namespace: namespace" in script_output
      subprocess.check_output("ray stop --force", shell=True)
  
imports: import os
  import subprocess
  import sys
  import warnings
  from unittest.mock import Mock, patch
  import pytest
  import ray
  import ray.client_builder
  import ray.util.client.server.server
  from ray._private.test_utils import run_string_as_driver, run_string_as_driver_nonblocking, wait_for_condition, skip_flaky_core_test_premerge
  from ray.util.state import list_workers
label_desc: Use image node_id 3 for calling a global function with example usage: test_namespace(ray_start_cluster) without return types