I've followed the tutorial from Debian (which is virtually identical to the one from Canonical) on how to set up unattended-upgrades, on an 18.04 server VM. I primarily want this for email update notifications, as a "set it and forget it" kind of thing. But when I do a dry-run of unattended-upgrade, I don't get an email notification. I read somewhere that some versions of unattended-upgrades don't send the email on a dry run.
How can I temporarily install an "old" package, and then let unattended-upgrades actually have something to upgrade? That seems like the most reliable way to test it.