title: Attributes are empty during unit test of a taglib in grails
body: <p>I am trying to test my code in taglib (grails 2.0.1):</p>
  
  <pre class="lang-java prettyprint-override"><code>class ATagLib {
      static namespace = "s"
      def person = {attrs, body -&gt; out &lt;&lt; attrs.person;}
  }
  
  @TestFor(ATagLib)
  class ATagLibTests {
     @Test
     void test() {
         String p = 'Joe'
         // None of these work for me.
         assert applyTemplate('&lt;s:person person="${p}"/&gt;') == 'Joe'
         assert applyTemplate('&lt;s:person/&gt;', [person:p]) == 'Joe'
     }
  }
  </code></pre>
  
  <p>The test always fails, because attrs.person is null. How do I properly set attributes?</p>