Added a missing test model.

models/CategoryNestedSet.php

+<?php
+class CategoryNestedSet extends Doctrine_Record
+{
+  public function setTableDefinition()
+  {
+    $this->setTableName('category_nested_set');
+    $this->hasColumn('id', 'integer', 4, array('primary' => true, 'autoincrement' => true));
+    $this->hasColumn('name', 'string', 255, array('notnull' => true));
+    
+    $this->actAs('NestedSet');
+  }
+
+  public function setUp()
+  {
+    
+  }
+}
\ No newline at end of file