This test did not support 'no auth' use case and other auth methods except 'login'. I fixed it by simply making the call to start() in the right way.
As shown in the source code of Net::SMTP (https://github.com/ruby/ruby/blob/ruby_2_5/lib/net/smtp.rb#L452), the start() function does accept the 'user' and 'secret' arguments. Also, in do_start() function (https://github.com/ruby/ruby/blob/ruby_2_5/lib/net/smtp.rb#L542), it automatically checks the auth method and args, skips the authentication if 'user' is not provided, and selects the right auth method from 'plain', 'login' or 'cram_md5'. This is exactly all of what we should do in a connection test and the odd 'auth_login' call in the previous code makes problems.
BTW, I am using 'localhost' as the third argument, which is the same as the default value in start(). This parameter is the domain address sent along with the 'ehlo' command in SMTP protocol. I have seen some documents, e.g. https://github.com/tpn/msmtp/blob/master/doc/msmtp.1#L455, saying that 'localhost' is fine. It works for me.
* FIX: rake emails:test to bypass the "STARTTLS required" message
* FIX: too much j
* hint meta.discourse.org to people with unknown errors from the mail test
Kelvin
Michael Brown
Sam
Jay Pfaffman
Gerhard Schlager
Régis Hanol