code: def test_as_multi_agent(self):
      env_class = make_multi_agent("CartPole-v0")
      env = env_class({"num_agents": 2})
  
      marl_module = DiscreteBCTorchModule(
          config=RLModuleConfig(
              env.observation_space,
              env.action_space,
              model_config_dict={"fcnet_hiddens": [32]},
          )
      ).as_multi_agent()
  
      self.assertNotIsInstance(marl_module, DiscreteBCTorchModule)
      self.assertIsInstance(marl_module, MultiAgentRLModule)
      self.assertEqual({DEFAULT_POLICY_ID}, set(marl_module.keys()))
  
      # check as_multi_agent() for the second time
      marl_module2 = marl_module.as_multi_agent()
      self.assertEqual(id(marl_module), id(marl_module2))
  
file_path: ray/rllib/core/rl_module/tests/test_marl_module.py
imports: import tempfile
  import unittest
  from ray.rllib.core.rl_module.rl_module import SingleAgentRLModuleSpec, RLModuleConfig
  from ray.rllib.core.rl_module.marl_module import MultiAgentRLModule, MultiAgentRLModuleConfig
  from ray.rllib.core.testing.torch.bc_module import DiscreteBCTorchModule
  from ray.rllib.core.testing.utils import DEFAULT_POLICY_ID
  from ray.rllib.env.multi_agent_env import make_multi_agent
  from ray.rllib.utils.test_utils import check
label_desc: Use image node_id 2 for calling the TestMARLModule obj's underlying member method code with example usage: obj.test_as_multi_agent() without return types