'Specifying no pairs same as specifying all.'

def test_tree_all_pairs_lowest_common_ancestor3(self):

    all_pairs = chain(combinations(self.DG, 2), ((node, node) for node in self.DG))
    ans = dict(tree_all_pairs_lca(self.DG, 0, all_pairs))
    self.assert_has_same_pairs(ans, self.ans)
