code: def test_negative(maxk=11):
      print("negative test")
  
      for k in range(4, maxk + 1):
          test_trees = list(nx.nonisomorphic_trees(k))
          start_time = time.time()
          trial = 0
          for i in range(len(test_trees) - 1):
              for j in range(i + 1, len(test_trees)):
                  trial += 1
                  assert (
                      tree_isomorphism(test_trees[i], test_trees[j])
                      == []
                  )
          print(k, trial, time.time() - start_time)
  
file_path: networkx/networkx/algorithms/isomorphism/tests/test_tree_isomorphism.py
imports: import random
  import time
  import pytest
  import networkx
  from networkx.algorithms.isomorphism.tree_isomorphism import rooted_tree_isomorphism, tree_isomorphism
  from networkx.classes.function import is_directed
label_desc: Use image node_id 9 for calling a global function with example usage: test_negative(maxk) without return types