Note: Most of this is already covered by Behat tests. The only thing that needs manual testing is the email update confirmation. Prerequisite Mailcatcher or an outgoing mail setup. Testing email change confirmation email - Multiple accounts with the same email disabled Log in as admin. Go to " Site administration / Plugins / Authentication / Manage authentication Make sure that " Allow accounts with same email " is unticked. Create a user with a username s1 and an email 's1@example.com' Create another user with a username s2 and an email 's2@example.com' On a separate browser window session (e.g. incognito window), log in as s1. Open another tab for Mailcatcher on s1's browser window. As s1, edit s1's email and change it to 'S1@EXAMPLE.COM' Save your changes. Confirm that you don't get any errors. Check the email update confirmation email on Mailcatcher. Open the link. Confirm that s1's email is now successfully changed to 'S1@EXAMPLE.COM' Edit s1's email address again and change it to 's11@example.com' Back on the admin's browser window, edit s2's profile and change the email to 's11@example.com' Back on s1's browser window, open the email change confirmation link. Confirm that you get an error that someone has already registered that email and that your email change has been cancelled. Testing email change confirmation email - Multiple accounts with the same email allowed Back on the admin's browser window, go to " Site administration / Plugins / Authentication / Manage authentication Tick " Allow accounts with same email " and save the changes. Back on s1's browser window, edit s1's email address again and change it to 's12@example.com' Back on the admin's browser window, edit s2's profile and change the email to 's12@example.com' Back on s1's browser window, open the email change confirmation link. Confirm that you are able to change s1's email address to 's12@example.com'