code: def test_dot_graph_defaults():
      # Test with default args.
      default_name = "mydask"
      default_format = "png"
      target = ".".join([default_name, default_format])
  
      ensure_not_exists(target)
      try:
          result = dot_graph(dsk)
          assert os.path.isfile(target)
          assert isinstance(result, Image)
      finally:
          ensure_not_exists(target)
  
imports: from __future__ import annotations
  import copy
  import os
  import re
  import sys
  from functools import partial
  from operator import add, neg
  import pytest
  from dask.dot import _to_cytoscape_json, cytoscape_graph
  from dask import delayed
  from dask.utils import ensure_not_exists
label_desc: Use image node_id 20 for calling a global function with example usage: test_dot_graph_defaults() without return types