How to I test actionmailer for failed delivery

I want to simulate a scenario where email sent using actionmailer has
failed. How do I induce mail delivery error in my tests ?

eg:

begin
UserNotify.deliver_signup(@user, params[‘user’][‘password’], url)
rescue
puts “user confirmation email error”
<…other code … >
end

I need to verify that user_confirmation_email_error is printed when
deliver_* method throws an exception