Function to test: https://github.com/wikimedia/mediawiki-extensions-Newsletter/blob/master/includes/NewsletterDb.php#L459

You can find instructions on how to test in the parent task description, or https://phabricator.wikimedia.org/T183613

Mentor: @01tonythomas, and others

Possibly, you might have to check the issue id, and if the operation went through well.