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: import pickle
  from collections import namedtuple
  import pytest
  from flash.core.serve.dag.task import flatten, get, get_dependencies, get_deps, istask, literal, preorder_traversal, quote, subs
  from flash.core.serve.dag.utils_test import add, inc
  from flash.core.utilities.imports import _TOPIC_SERVE_AVAILABLE
label_desc: Use image node_id 13 for calling a global function with example usage: test_subs() without return types