Make test suite generate files outside of the source tree

[larseggert]

Description

The tests seem to generate directories in the source tree names tmp-* and they also seem to generate files under test/media and possibly test in general.

It would be nice if that as reworked so all that happened under /tmp.

Code of Conduct

• I agree to follow the IETF's Code of Conduct

[rjsparks]

or at least outside /workspace. /tmp brings its own dragons, as we saw with the html validation code.