code: def test_functions_of():
      a = lambda x: x
      b = lambda x: x
      assert functions_of((a, 1)) == {a}
      assert functions_of((a, (b, 1))) == {a, b}
      assert functions_of((a, [(b, 1)])) == {a, b}
      assert functions_of((a, [[[(b, 1)]]])) == {a, b}
      assert functions_of(1) == set()
      assert functions_of(a) == set()
      assert functions_of((a,)) == {a}
  
imports: from __future__ import annotations
  import itertools
  import pickle
  from functools import partial
  import pytest
  import dask
  from dask.base import tokenize
  from dask.core import get_dependencies
  from dask.local import get_sync
  from dask.optimization import SubgraphCallable, cull, functions_of, fuse, fuse_linear, inline, inline_functions
  from dask.utils import apply, partial_by_order
  from dask.utils_test import add, inc
label_desc: Use image node_id 17 for calling a global function with example usage: test_functions_of() without return types