code: def test_to_graphviz_collapse_outputs():
      g = to_graphviz(dsk, collapse_outputs=True)
      labels = list(filter(None, map(get_label, g.body)))
      assert len(labels) == 6  # 6 nodes total
      assert set(labels) == {"c", "d", "e", "f", '""'}
      shapes = list(filter(None, map(get_shape, g.body)))
      assert set(shapes) == {"box", "circle"}
  
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 13 for calling a global function with example usage: test_to_graphviz_collapse_outputs() without return types