code: def test_dot_graph_no_filename(tmpdir, format, typ):
      before = tmpdir.listdir()
      result = dot_graph(dsk, filename=None, format=format)
      # We shouldn't write any files if filename is None.
      after = tmpdir.listdir()
      assert before == after
      assert isinstance(result, typ)
  
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 19 for calling a global function with example usage: test_dot_graph_no_filename(tmpdir, format, typ) without return types