use new logmsg and set --show in tests

Also modify `logmsg` to output additional separator lines to make the
demarcation between tests even clearer.

tests/test_functions/logmsg.fish

@@ -1,4 +1,9 @@
 function logmsg
+    echo
+    echo "####################"
     echo "# $argv"
+
+    echo >&2
+    echo "####################" >&2
     echo "# $argv" >&2
 end