code: def test_tree_all_pairs_lca_default_root(self):
      assert dict(tree_all_pairs_lca(self.DG)) == self.ans
  
imports: from itertools import chain, combinations, product
  import pytest
  import networkx
label_desc: Use image node_id 3 for calling the TestTreeLCA obj's underlying member method code with example usage: obj.test_tree_all_pairs_lca_default_root() without return types