code: def test_subs():
      assert subs((sum, [1, "x"]), "x", 2) == (sum, [1, 2])
      assert subs((sum, [1, ["x"]]), "x", 2) == (sum, [1, [2]])
  
imports: from __future__ import annotations
  import pickle
  from collections import namedtuple
  import pytest
  from dask.core import flatten, get, get_dependencies, get_deps, getcycle, has_tasks, ishashable, iskey, istask, literal, preorder_traversal, quote, subs, validate_key
  from dask.utils_test import GetFunctionTestMixin, add, inc
label_desc: Use image node_id 19 for calling a global function with example usage: test_subs() without return types