docstr: Test warning when bucket utilization is low
code: def test_bucket_low_utilization_warning(self):
      """Test warning when bucket utilization is low"""
      layer_size = 2 * 1024 * 1024
      num_layers = 4
      fairish_bucket_cap_mb = (
          4 * num_layers * layer_size / (1024 * 1024)
      )
  
      # Check that warning is raised when bucket utilization is low
      with self.assertWarnsRegex(
          Warning, ".*Consider decreasing the bucket_cap_mb argument."
      ):
          self.test_matches_pytorch(
              num_layers=num_layers,
              layer_size=layer_size,
              bucket_cap_mb=fairish_bucket_cap_mb * 2,
              contiguous_buffers=True,
          )
  
      # Check that warning is not raised when bucket utilization is high
      with warnings.catch_warnings(record=True) as warns:
          self.test_matches_pytorch(
              num_layers=num_layers,
              layer_size=layer_size,
              bucket_cap_mb=fairish_bucket_cap_mb,
              contiguous_buffers=True,
          )
          for w in warns:
              self.assertNotRegex(
                  str(w.message),
                  ".*Consider decreasing the bucket_cap_mb argument.",
              )
  
imports: from contextlib import contextmanager
  import io
  from typing import Callable, Optional, Tuple
  import unittest
  import warnings
  import torch
  from torch.testing._internal import common_utils
  from apex.transformer.testing.distributed_test_base import NcclDistributedTestBase
label_desc: Use image node_id 23 for calling the TestDistributedFusedAdam obj's underlying member method code with example usage: obj.test_bucket_low_utilization_warning() without return types