title: Validate_presence_of test passing when it shouldn't?
body: <p>I just started using RSpec and Shoulda-matchers, and I think something is going wrong here.</p>
  
  <p>In my model, I have a member, displayname, that is validated like this.</p>
  
  <pre><code>validates :displayname, :presence =&gt; false #just for this test.
  </code></pre>
  
  <p>In my spec, i wrote this</p>
  
  <pre><code>it { should validate_presence_of(:displayname) }
  </code></pre>
  
  <p>Yet it's passing. Shouldn't that fail unless i switch should to should not? </p>
  
  <p>edit: it seems to just be behaving like i said to validate the presence, whether i say true or false. I changed it to should_not and started failing unless i completely removed the presence check. Is the behavior of validates presence to just not use whatever bool you pass it?</p>