Comment 21 for bug 2015420

Now, to the actual functionality test on Xenial:

Xenial is an EOSS release, so messages about esm-infra will be present in MOTD by default.
After creating the marker file and triggering an update of MOTD, those messages disappear, but the updates count remains.

root@xenial-sut:~# apt policy update-notifier-common
update-notifier-common:
  Installed: 3.168.22
  Candidate: 3.168.22
  Version table:
 *** 3.168.22 500
        500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     3.168.20 500
        500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
     3.168.15 500
        500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
     3.168.7 500
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
     3.168 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
root@xenial-sut:~# run-parts /etc/update-motd.d/
Welcome to Ubuntu 16.04.7 LTS (GNU/Linux 6.5.0-21-generic x86_64)

 * Documentation: https://help.ubuntu.com
 * Management: https://landscape.canonical.com
 * Support: https://ubuntu.com/pro

Expanded Security Maintenance for Infrastructure is not enabled.

9 updates can be applied immediately.
To see these additional updates run: apt list --upgradable

206 additional security updates can be applied with ESM Infra.
Learn more about enabling ESM Infra service for Ubuntu 16.04 at
https://ubuntu.com/16-04

New release '18.04.6 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

root@xenial-sut:~# touch /var/lib/update-notifier/hide-esm-in-motd
root@xenial-sut:~# rm /var/lib/update-notifier/updates-available
root@xenial-sut:~# apt update
Hit:1 http://archive.ubuntu.com/ubuntu xenial InRelease
Hit:2 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit:4 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Hit:5 http://archive.ubuntu.com/ubuntu xenial-proposed InRelease
Reading package lists... Done
Building dependency tree
Reading state information... Done
6 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@xenial-sut:~# run-parts /etc/update-motd.d/
Welcome to Ubuntu 16.04.7 LTS (GNU/Linux 6.5.0-21-generic x86_64)

 * Documentation: https://help.ubuntu.com
 * Management: https://landscape.canonical.com
 * Support: https://ubuntu.com/pro

9 updates can be applied immediately.
To see these additional updates run: apt list --upgradable

New release '18.04.6 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

I am marking this bug verification-done on Xenial.