This test fails because it expects a MIME type "Content-Type: image/gif"
whereas that provided by libmagic is "Content-Type: image/gif; charset=binary"
Presumably the test was written against a different version.
--- aegis-4.24/test/02/t0228a-matt.sh	2008-03-14 07:19:27.000000000 +0100
+++ aegis-4.24/test/02/t0228a-matt.sh	2014-01-27 09:43:44.000000000 +0100
@@ -147,7 +147,8 @@
 SCRIPT_NAME=/cgi-bin/aeget \
 PATH_INFO=icon/rss.gif \
 QUERY_STRING= \
-$bin/aeget > rss.served.gif 2>&1
+$bin/aeget \
+| sed -e 's%^Content-Type: image/gif; charset=binary%Content-Type: image/gif%' > rss.served.gif 2>&1
 if test $? -ne 0 ; then fail; fi
 
 # Compare the expected and the actual received file.
f68fb9a3'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>refs</a><a class='active' href='/guix/log/gnu/packages/usb-modeswitch.scm'>log</a><a href='/guix/tree/gnu/packages/usb-modeswitch.scm?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>tree</a><a href='/guix/commit/gnu/packages/usb-modeswitch.scm?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>commit</a><a href='/guix/diff/gnu/packages/usb-modeswitch.scm?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/usb-modeswitch.scm'>
<input type='hidden' name='id' value='041a12c46b77094c3a89276cf55d9cf1f68fb9a3'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>root</a>/<a href='/guix/log/gnu?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>gnu</a>/<a href='/guix/log/gnu/packages?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>packages</a>/<a href='/guix/log/gnu/packages/usb-modeswitch.scm?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3'>usb-modeswitch.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/usb-modeswitch.scm?id=041a12c46b77094c3a89276cf55d9cf1f68fb9a3&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-07-14 03:25:04 +0200'>2020-07-14</span></td><td><a href='/guix/commit/gnu/packages/usb-modeswitch.scm?id=9cb208d86b0fae4b5c2b9ef4fa38a43594434c78'>gnu: usb-modeswitch: Use CC-FOR-TARGET.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/usb-modeswitch.scm (usb-modeswitch)[arguments]: Use
CC-FOR-TARGET.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-07-14 03:25:04 +0200'>2020-07-14</span></td><td><a href='/guix/commit/gnu/packages/usb-modeswitch.scm?id=dbfd8044254f794c7ee56ae275522674e180bc9c'>gnu: usb-modeswitch: Update to 2.6.1.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/usb-modeswitch.scm (usb-modeswitch): Update to 2.6.1.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>