/**
  * Method to test the username for uniqueness.
  *
  * @param   SimpleXMLElement  $element  The SimpleXMLElement object representing the <field /> tag for the form field object.
  * @param   mixed             $value    The form field value to validate.
  * @param   string            $group    The field name group control value. This acts as as an array container for the field.
  *                                      For example if the field has name="foo" and the group value is set to "bar" then the
  *                                      full field name would end up being "bar[foo]".
  * @param   JRegistry         $input    An optional JRegistry object with the entire data set to validate against the entire form.
  * @param   JForm             $form     The form object for which the field is being tested.
  *
  * @return  boolean  True if the value is valid, false otherwise.
  *
  * @since   11.1
  */
 public function test(SimpleXMLElement $element, $value, $group = null, Registry $input = null, Form $form = null)
 {
     // Get the database object and a new query object.
     $db = Factory::getDBO();
     $query = $db->getQuery(true);
     // Build the query.
     $query->select('COUNT(*)');
     $query->from('#__users');
     $query->where('username = '******'id') : '';
     $query->where($db->quoteName('id') . ' <> ' . (int) $userId);
     // Set and query the database.
     $db->setQuery($query);
     $duplicate = (bool) $db->loadResult();
     if ($duplicate) {
         return false;
     }
     return true;
 }