'Specifying only some pairs gives only those pairs.'

def test_tree_all_pairs_lowest_common_ancestor2(self):

    test_pairs = [(0, 1), (0, 1), (1, 0)]
    ans = dict(tree_all_pairs_lca(self.DG, 0, test_pairs))
    assert_true((((0, 1) in ans) and ((1, 0) in ans)))
    assert_equal(len(ans), 2)
