docstr: Test is_singleton_tensor function
docstr_tok: ["Test","is_singleton_tensor","function"]
code: def test_is_singleton_tensor(self):
      """Test is_singleton_tensor function"""
      assert is_singleton_tensor(torch.tensor(4.0))
      assert not is_singleton_tensor(torch.tensor([4.0]))
      assert not is_singleton_tensor(torch.tensor([4.0, 5.0]))
      assert not is_singleton_tensor([4.0])
      assert not is_singleton_tensor(4.0)
  
imports: import copy
  import functools
  from time import time
  import unittest
  from parameterized import parameterized
  import torch
  from torch import nn
  from torch.optim import SGD, Adadelta, Adam
  from fairscale.fair_dev.testing.testing import dist_init, objects_are_equal, spawn_for_all_world_sizes
  from fairscale.internal.params import recursive_copy_to_device
  from fairscale.nn.data_parallel import FullyShardedDataParallel, get_fsdp_instances
  from fairscale.nn.data_parallel.fsdp_optim_utils import is_singleton_tensor
  from .test_fsdp import DistributedTest, DummyProcessGroup, MixtureOfExperts, TransformerWithSharedParams, rename_test, spawn_and_init
label_desc: Use image node_id 7 for calling the TestOptimizerUtils obj's underlying member method code with example usage: obj.test_is_singleton_tensor() without return types