Arsse/tests/docroot/Feed/Discovery/Feed.php

<?php return [
    'mime'    => "application/rss+xml",
    'content' => <<<MESSAGE_BODY
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/">
<channel>
    <title>Test feed</title>
    <link>http://localhost:8000/</link>
    <description>Example newsfeed title</description>
</channel>
</rss>
MESSAGE_BODY
];