I think the "test" specs parsed from /etc/mailcap are not being tried.
On a tty with DISPLAY unset I find gnus trying to run xpdf (or
acroread), despite having

	test=test -n "$DISPLAY"

I think the info alists in mailcap-mime-data are getting strings
"test" rather than symbols `test', which is making those tests invisible
to mailcap-viewer-passes-test and mailcap-mailcap-entry-passes-test
(those funcs call "(assq 'test info)").

2006-01-21  Kevin Ryde  <user42@zip.com.au>

        * mailcap.el (mailcap-parse-mailcap-extras): "test" key must go into
        alists as symbol not string, since that's what
        mailcap-viewer-passes-test and mailcap-mailcap-entry-passes-test look
        for.

I'd have thought symbols for all keys would be the way to go, but I
see "copiousoutput", "needsx11" and friends are getting tested/used as
strings at the moment.