code: def test_all_pairs_lca_pairs_without_lca(self):
      G = self.DG.copy()
      G.add_node(-1)
      gen = all_pairs_lca(G, [(-1, -1), (-1, 0)])
      assert dict(gen) == {(-1, -1): -1}
  
imports: from itertools import chain, combinations, product
  import pytest
  import networkx
label_desc: Use image node_id 8 for calling the TestDAGLCA obj's underlying member method code with example usage: obj.test_all_pairs_lca_pairs_without_lca() without return types