Also add test for `flat_multiset` to avoid regression. --------- Co-authored-by: Hui Xie <hui.xie1990@gmail.com> Co-authored-by: A. Jiang <de34@live.cn>
Also add test for `flat_multiset` to avoid regression. --------- Co-authored-by: Hui Xie <hui.xie1990@gmail.com> Co-authored-by: A. Jiang <de34@live.cn>