title: rspec shoulda syntax for model.errors
body: <p>I get the following error message for the code below:</p>
  
  <pre><code> Failure/Error: @league.errors.on(:short_name).should_equal "can't be blank"
   NoMethodError:
     undefined method `on' for #&lt;ActiveModel::Errors:0x000001017853f0&gt;
  
  
  @league.errors.on(:short_name).should_equal "can't be blank"
  </code></pre>
  
  <p>According to several documentation references that I am reading, this should work.  Any idea what's going on?</p>