Message ID in mailer is different for same email in unit test

Hi,

I have a problem writing unit tests for the mailer.

I posted it on Message ID in mailer is different for same email in unit test · Issue #8128 · rails/rails · GitHub where the bug
was
quickly closed, but no solution was given (only saying it was my
fault…).

So I am reposting here.

The main problem is that except for the Message ID (as far as I can see,
I
looked multiple times to the two differences in the string but they seem
to
match completely) two mails generated are the same (but the unit tests
fails).
I followed this Testing Rails Applications — Ruby on Rails Guides
guide.

If I am doing something wrong: please point it out to me.

Cheers,
Nathan