Test notification e-mails (e.g. pipeline failures)
From gitlab-org/gitlab#36201 (comment 244125604), we had a significant regression due to differences between a development and production environments. We can try to eliminate those differences, but we should also have end-to-end tests to ensure e-mail notifications work from release to release. How this might work:
- Configure the SMTP provider to send to MailHog (https://hub.docker.com/r/mailhog/mailhog)
- Use the MailHog API to confirm the e-mail was sent properly