On Thu, 13 May 2021, Frank Cox wrote:
According to the manual you need to use the "HP Toolbox" to access the test page function (and other stuff).
https://www.manualsdir.com/manuals/398954/hp-deskjet-d1420-printer.html?page...
http://manpages.ubuntu.com/manpages/trusty/man1/hp-toolbox.1.html
This appears to be part of hplip, which is available in the standard Centos repository.
Thanks. The first link got me to something that was Windows-only.