code: def test_default_serializer():
      assert isinstance(get_default_serializer(), TorchSerializer)
      set_default_serializer(JsonSerializer())
      assert isinstance(get_default_serializer(), JsonSerializer)
      set_default_serializer(TorchSerializer())
  
file_path: nni/test/ut/nas/test_utils.py
imports: import tempfile
  import pytest
  from pathlib import Path
  import torch
  from nni.nas.utils import *
label_desc: Use image node_id 2 for calling a global function with example usage: test_default_serializer() without return types