code: def test_metadata_exists(self) -> None:
      app_state = {"module": nn.Linear(2, 2)}
      with tempfile.TemporaryDirectory() as temp_dir:
          dirpath = os.path.join(temp_dir, "checkpoint")
          Snapshot.take(dirpath, app_state=app_state)
  
          fs = get_filesystem(dirpath)
          self.assertTrue(
              _metadata_exists(fs, dirpath, SNAPSHOT_METADATA_FNAME)
          )
  
          os.remove(os.path.join(dirpath, SNAPSHOT_METADATA_FNAME))
          self.assertFalse(
              _metadata_exists(fs, dirpath, SNAPSHOT_METADATA_FNAME)
          )
  
imports: import os
  import shutil
  import tempfile
  import unittest
  import torch
  import torch.distributed
  from torch import nn
  from torch.distributed import launcher
  from torchsnapshot import Snapshot
  from torchsnapshot.snapshot import SNAPSHOT_METADATA_FNAME
  from torchtnt.framework._test_utils import DummyTrainUnit, get_dummy_train_state
  from torchtnt.framework.callbacks._checkpoint_utils import _delete_checkpoint, _metadata_exists, _prepare_app_state_for_checkpoint, _retrieve_checkpoint_dirpaths, get_checkpoint_dirpaths, get_latest_checkpoint_path, rank_zero_read_and_broadcast
  from torchtnt.utils.distributed import get_global_rank, PGWrapper
  from torchtnt.utils.env import init_from_env
  from torchtnt.utils.fsspec import get_filesystem
  from torchtnt.utils.test_utils import get_pet_launch_config, spawn_multi_process
label_desc: Use image node_id 10 for calling the CheckpointUtilsTest obj's underlying member method code with example usage: obj.test_metadata_exists() without return types