factory_girl

https://github.com/thoughtbot/factory_girl

Ruby

A library for setting up Ruby objects as test data.

Mail::Message#add_message_id

Creates a new empty Message-ID field and inserts it in the correct order
into the Header.  The MessageIdField object will automatically generate
a unique message ID if you try and encode it or output it to_s without
specifying a message id.

It will preserve the message ID you specify if you do.

Source | Google | Stack overflow

Edit

git clone [email protected]:thoughtbot/factory_girl.git
cd factory_girl
open

Contribute

# Make a new branch

git checkout -b -your-name--update-docs-Mail--Message-add_message_id-for-pr

# Commit to git

git add git commit -m "better docs for Mail::Message#add_message_id"

# Open pull request

gem install hub # on a mac you can `brew install hub`

hub fork

git push <your name> -your-name--update-docs-Mail--Message-add_message_id-for-pr

hub pull-request

# Celebrate!