public function testNested()
 {
     $nested = Model\Category::nested()->get();
     $iteratorArray = new RecursiveArrayIterator($nested);
     $iterator = new RecursiveIteratorIterator($iteratorArray);
     $this->assertTrue($iterator->valid());
     $this->assertFalse($nested == $this->categories);
     $parent_id = $this->_get_random_parent_id($iteratorArray);
     if ($parent_id) {
         $result = $this->_helper_recursive($nested, $parent_id);
         $this->assertGreaterThan(0, $result);
     }
 }