title: SitePrism gem- how to set_url dynamically based on the environment?
body: <p>I'm converting the in-browser tests for an app to use the SitePrism gem.  In the gem readme, I see the following:</p>
  
  <pre><code>A page usually has a URL. If you want to be able to navigate to a page, you'll need to set its URL. Here's how:
  
      class Home &lt; SitePrism::Page
        set_url "http://www.google.com"
      end
  
  If you've set Capybara's app_host then you can set the URL as follows:
  
      class Home &lt; SitePrism::Page
        set_url "/home.htm"
      end
  </code></pre>
  
  <p>I anticipate needing to run these tests in multiple environments (i.e. locally, and on a staging server).  I'm wondering how I would call Capybara's app_host method dynamically.  Would I add something like this to my spec_helper file?</p>
  
  <pre><code>Capybara.app_host = ENV[URL]
  </code></pre>
  
  <p>Thanks.</p>