title: Rails - How to add a format to an url helper?
body: <p>how can I make an URL helper create an URL in a given request/response format?</p>
  
  <p>For example, in my test I have the following:</p>
  
  <pre><code>get(activity_url(activity))
  </code></pre>
  
  <p>This will returns me an HTML on the <code>@response</code> object. I'm looking to have the same behavior of the following:</p>
  
  <pre><code>get({controller: 'activities', action: 'show', id: activity.id, format: 'js'})
  </code></pre>
  
  <p>but without all this wording. Is it possible?</p>