docstr: Test if indepent sampling yields a MultiAgentBatch with the
  correct policy id.
docstr_tok: ["Test","if","indepent","sampling","yields","a","MultiAgentBatch","with","the","correct","policy","id","."]
code: def test_policy_id_of_multi_agent_batches_independent(self):
      """Test if indepent sampling yields a MultiAgentBatch with the
      correct policy id."""
      self.batch_id = 0
  
      # Test lockstep mode with different policy ids using MultiAgentBatches
      buffer = MultiAgentReplayBuffer(
          capacity=10,
          replay_mode="independent",
          num_shards=1,
      )
  
      self._add_multi_agent_batch_to_buffer(
          buffer, num_policies=1, num_batches=1
      )
  
      mabatch = buffer.sample(1)
      assert list(mabatch.policy_batches.keys())[0] == 0
  
file_path: ray/rllib/utils/replay_buffers/tests/test_multi_agent_replay_buffer.py
imports: import unittest
  import numpy
  from ray.rllib.policy.sample_batch import SampleBatch, MultiAgentBatch, concat_samples
  from ray.rllib.policy.sample_batch import DEFAULT_POLICY_ID
  from ray.rllib.utils.replay_buffers.multi_agent_replay_buffer import MultiAgentReplayBuffer
  from ray.rllib.utils.replay_buffers.prioritized_replay_buffer import PrioritizedReplayBuffer
  from ray.rllib.utils.replay_buffers.replay_buffer import ReplayBuffer
label_desc: Use image node_id 3 for calling the TestMultiAgentReplayBuffer obj's underlying member method code with example usage: obj.test_policy_id_of_multi_agent_batches_independent() without return types