'Handles invalid input correctly.'

def test_tree_all_pairs_lowest_common_ancestor5(self):

    empty_digraph = tree_all_pairs_lca(nx.DiGraph())
    assert_raises(nx.NetworkXPointlessConcept, list, empty_digraph)
    bad_pairs_digraph = tree_all_pairs_lca(self.DG, pairs=[((-1), (-2))])
    assert_raises(nx.NodeNotFound, list, bad_pairs_digraph)
