Fix a regression and improve content when sending test e-mails.
Review Request #11353 — Created Dec. 28, 2020 and submitted
Some cleanup work in the e-mail settings page resulted in the wrong
keyword argument being used when sending a test e-mail. We were passing
from_email. We didn't have any unit tests
covering this, and it wasn't caught in development.
This change fixes up the keyword argument and adds a test suite. It also
improves upon the e-mail's subject, body, and error handling. The new
content more explicitly lists the product in the summary, adds a
confirmation that things look good in the body, includes recipient
information in the logs, and an error message in the message shown in
Unit tests pass.