The version of ActionMailer included with Rails 3.0.4 allows you to use named routes in the mailer view by default, but writing a functional test that tests those named routes isn’t as out-of-the-box.

Say you had created a “Notifications” object with a subscribe method, like such:

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class Notifications < ActionMailer::Base
  def subscribe(user)
    mail(:to      => 'test@example.com',
   :subject => "You are now subscribed")
  end
end

The subscribe method creates a simple text email format that includes a link back to your application:

Thanks for subscribing. Would you like to unsubscribe?
<%= unsubscribe_url(:email => 'test@example.com') %>

Here is what a test that checks that the important unsubscribe link exists might look like:

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require 'test_helper'

class NotificationsTest < ActionMailer::TestCase
  test "subscribe" do
    mail = Notifications.subscribe
    assert_match unsubscribe_url(:email => 'test@example.com'), mail.body.encoded
  end
end

However, running that test will give you an error like:

NoMethodError: undefined method `unsubscribe_url' for #<NotificationsTest:0x000001039dbe40>
    test/functional/notifications_test.rb:6:in `block in <class:NotificationsTest>'

To get around this, you need to include the URL helpers (to define those methods) and point to your default URL options (to define options such as the default host). Modify the test to look like:

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require 'test_helper'

class NotificationsTest < ActionMailer::TestCase
  include Rails.application.routes.url_helpers

  def default_url_options
    Rails.application.config.action_mailer.default_url_options
  end

  test "subscribe" do
    mail = Notifications.subscribe
    assert_match unsubscribe_url(:email => 'test@example.com'), mail.body.encoded
  end
end