This test requires administrator access.
1) Navigate to Site administration>Users>Accounts>Add a new user.
2) Create a new user, for example with the username bobexample and the email email@example.com. Log out.
3) Log in as the new user, using the username bobexample. Verify you can log in. Log out.
4) Log in with the email firstname.lastname@example.org and verify you CANNOT log in.
5) Log back in as administrator and navigate to Site administration>Plugins>authentication>Manage authentication. Scroll down and check 'Allow login via email' (authloginviaemail). Save and log out.
6) Repeat step 3, verifying you can still log in with the username bobexample.
7) Repeat step 4, verifying you now CAN log in with the email email@example.com