title: Testing helper in rspec with I18n lazy lookup
body: <p>Consider this example. I have a Product model which has <code>discount_percentage</code>. And we're maintaining multiple locales. In the view we do not want the i18n stuff mess up the view. So we make a helper to read better and probably reuse it in other views: <code>render_product_discount</code> (code please see below) which will render the discount status of this product. And we use i18n lazy lookup feature throughout the application. But when we want to test this helper method we get a Error:</p>
  
  <pre><code># RuntimeError:
  # Cannot use t(".product_discount") shortcut because path is not available
  </code></pre>
  
  <p>because there is no <code>path</code> available for translation helper to expand the lazy translation key.</p>
  
  <p>Expected Output: This product has 20% discount.</p>
  
  <p>Helper name: <code>render_product_discount</code></p>
  
  <pre><code>def render_product_discount
    t('.product_discount', discount_percentage: product.discount_percentage)
  end
  
  # es.yml
  es:
    products:
      show:
        product_discount: Este producto tiene un %{discount_percentage} descuento.
  
  # en.yml
  en:
    products:
      show:
        product_discount: This product has %{discount_percentage} discount.
  </code></pre>
  
  <p>How to workaround this? Thanks in advance.</p>