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.
><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>
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<tr><td><span title='2022-12-26 09:34:26 +0100'>2022-12-26</span></td><td><a href='/guix/commit/gnu/system/images/wsl2.scm?id=c50cd1bbece27097456242f246f89c053e7cc1a2'>images: wsl2: Create XDG_RUNTIME_DIR on first login.</a><span class='msg-avail'>...</span></td><td>dan</td></tr>
<tr><td><span title='2022-10-13 17:41:59 +0200'>2022-10-13</span></td><td><a href='/guix/commit/gnu/system/images/wsl2.scm?id=9c976474465f055f0b3ceb7877a53ae1cad22613'>system: Use a valid license as the dummy license.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2022-09-24 14:49:09 +0200'>2022-09-24</span></td><td><a href='/guix/commit/gnu/system/images/wsl2.scm?id=c8112f3bd95269ce4aca12dedbfe61bb6b37acae'>system: images: Add wsl2 module.</a><span class='msg-avail'>...</span></td><td>Alex Griffin</td></tr>