I think it is useful to extract as much as possible out of your Mailman::Application
block and put it into your app somewhere. Then test that processing.
This Railscast (pro-only, sorry) has an example of "An Alternative to Routing" that is pretty good.
Basically instead of doing something like:
Mailman::Application.run do
subject(/Update (\d+)/) do |ticket_id|
...
you just say:
Mailman::Application.run do
default do
MailProcessor.receive_mail(message)
end
end
Then the MailProcessor
class would handle reading the message and calling the right other functions in your app (depending on the message's subject, recipient, sender, etc.) I would then RSpec test the MailProcessor
class for doing the right thing.
This is similar to how I approach testing rake tasks (put the functionality in a lib file that you test, and have the rake task just call the lib file.) Then you can be fairly certain that the functionality is being tested properly. If you were paranoid about the rake task, you can try an approach like: http://robots.thoughtbot.com/post/11957424161/test-rake-tasks-like-a-boss.