For Atom feeds, I have my own template and a few custom filters. I don't use jekyll-feed because I sometimes want an entry to link somewhere other than my site (Daring Fireball-style link posts), and that's not supported.
If I want a post to link elsewhere, I add link
to the post frontmatter:
title: "A validator for RSS and Atom feeds"
layout: "post"
date: "2017-09-22 08:19:42 +0100"
link: "https://github.com/rubys/feedvalidator"
Because I'm rolling my own feeds, I use rubys/feedvalidator to test I'm really producing valid Atom markup.
See tests/test_atom_feed.py
.