Testing email reception

Is there a library for testing email reception? Something like:

emailer.sendWelcomeEmail('new_user@example.com') // sends an email containing 'welcome' 
assert(emailChecker.receivedEmailMatching('new_user@example.com', 'welcome!'))

I know I can implement this through checking a real mailbox, but I'm looking for something with a full-featured API, and easy clearing/reading of mailbox contents.

Ideally a node library.