title: Rspec raise_error test failing even though the method raises an error
body: <p>My test looks like this:</p>
  
  <p><code>it 'does return an error when passing a non-subscription or trial membership' do
      expect(helper.description_for_subscription(recurring_plan)).to raise_error(RuntimeError)
  end</code></p>
  
  <p>My method returns this:</p>
  
  <p><code>fail 'Unknown subscription model type!'</code></p>
  
  <p>Yet Rspec comes back with this failure message:</p>
  
  <p><code>Failure/Error: expect(helper.description_for_subscription(recurring_plan)).to raise_error(RuntimeError)
       RuntimeError:
         Unknown subscription model type!</code></p>
  
  <p>What is going on??</p>