title: Laravel 5.5 On demand notification with slack
body: <p>According to <a href="https://laravel.com/docs/5.5/notifications#on-demand-notifications" rel="noreferrer">this page</a>, we can send a notification on demand without going through a model. How do I do the same using slack?</p>
  
  <p>I want to do something like this:</p>
  
  <pre><code>$emailAddress = 'my email address';
  Notification::route('mail', $emailAddress)
              -&gt;route('slack', 'what do I put here?')
              -&gt;notify(new TestNotification());
  </code></pre>
  
  <p>The code works without the <code>slack</code> line.</p>
  
  <p>Edit: <a href="https://stackoverflow.com/questions/46277323/laravel-testing-on-demand-notification">this StackOverflow question</a> uses the on demand method</p>