code: def test_tree_all_pairs_lca_trees_without_LCAs(self):
      G = nx.DiGraph()
      G.add_node(3)
      ans = list(tree_all_pairs_lca(G))
      assert ans == [((3, 3), 3)]
  
imports: from itertools import chain, combinations, product
  import pytest
  import networkx
label_desc: Use image node_id 15 for calling the TestTreeLCA obj's underlying member method code with example usage: obj.test_tree_all_pairs_lca_trees_without_LCAs() without return types