title: Validates with :if
body: <p>I'm trying to create a condition in which the attribute 'one' is zero and the attribute 'two' is one, then a model is not valid. But when I make:</p>
  
  <pre><code>Model.create(:one =&gt; 1, :two =&gt; 0).valid?
  </code></pre>
  
  <p>The unit test returns <code>true</code>! Why?</p>
  
  <pre><code>validates :one, :two, :presence =&gt; true, :if =&gt; :if condition_testing?
  
  def condition_testing?
      !(one == 0 &amp;&amp; two == 1)
  end
  </code></pre>