/**
  * Called after fields are validated.
  * 
  * @param object $obj Object being validated.
  * @access private
  */
 protected function _post_validate($obj)
 {
     parent::_post_validate($obj);
     /** @var DATE_TIME $test */
     $test = $this->value_for('time_testing_scheduled');
     /** @var DATE_TIME $ship */
     $ship = $this->value_for('time_scheduled');
     if ($test->is_valid() && $ship->is_valid()) {
         if (!$test->less_than_equal($ship)) {
             $this->record_error('time_testing_scheduled', 'Test date must be before or on ship date.');
         }
     }
 }