title: Deliver later not working in the test environment in Rails 5
body: <p>Basically, with the test config set up exactly how it worked in Rails 4 (delivery method set as test etc), aside from deprecated options which I have replaced, mail only sends with deliver_now, not deliver_later. Deliver_later works in the development environment, even when the config is identical between the two environments.</p>
  
  <p>Test environment mailer config:</p>
  
  <pre><code>config.action_mailer.delivery_method = :test
  config.action_mailer.perform_deliveries = true
  config.action_mailer.perform_caching = false
  config.action_mailer.raise_delivery_errors = true
  config.action_mailer.default_url_options = { :host =&gt; 'localhost:3000' }
  </code></pre>