Rendering emails locally is a pain. Rendering all the emails in your Rails app is even more of a headache.
I frequently get requests from clients to send them a complete set of the emails sent from their applications for copywriting review. I wrote a quick gem for you to incorporate that function into your ActionMailer tests. It will log all of your emails to a central location so that you can zip them up and send them to your clients and/or stakeholders.
I've called it postmaster_general.
Once installed (add it to your gemfile as specified in the README, set the log directory like so:
PostmasterGeneral.log_directory = "/some/arbitrary/path"
Then, you might have an ActionMailer spec like this:
After you run your suite or this particular spec, you'll have a file with a path of /some/arbitrary/path/a_delivery.txt that contains the contents of your message. What's neat is it works well with continuous integration - you could set up your CI to automatically prepare an up to date version of all the emails in your system.
I hope you find it helpful, and that it encourages you to write ActionMailer tests!