title: PhpStorm autocompletion in traits
body: <p>I have a trait that must always be mixed in to a subclass of <code>\PHPUnit_Framework_TestCase</code>. PhpStorm doesn't know this. Is there anything I can do to get PhpStorm to autocomplete and "typecheck" things like <code>assertNull</code> inside the trait?</p>
  
  <pre><code>&lt;?php
  trait MyTestUtils
  {
      public function foo()
      {
          $this-&gt;assertNu // autocomplete?
      }
  }
  </code></pre>
  
  <p>The best I could come up with so far is putting the following in each method:</p>
  
  <pre><code>/** @var \PHPUnit_Framework_TestCase|MyTestUtils $this */
  </code></pre>
  
  <p>But this is repetitive and doesn't understand protected memebers. Is there a better option?</p>