Method test

/**
 * Method to test the validity of a Joomla User.
 *
 * @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 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   ?Registry          $input    An optional Registry object with the entire data set to validate against the entire form.
 * @param   ?Form              $form     The form object for which the field is being tested.
 *
 * @return  boolean  True if the value is valid, false otherwise.
 *
 * @since   4.0.0
 */
public function test(\SimpleXMLElement $element, $value, $group = null, Registry $input = null, Form $form = null)
{
    // Check if the field is required.
    $required = (string) $element['required'] === 'true' || (string) $element['required'] === 'required';
    // If the value is empty, null or has the value 0 and the field is not required return true else return false
    if ($value === '' || $value === null || (string) $value === '0') {
        return !$required;
    }
    // Get the database object and a new query object.
    $db = Factory::getDbo();
    $query = $db->getQuery(true);
    // Build the query.
    $query->select('COUNT(*)')->from($db->quoteName('#__users'))->where($db->quoteName('id') . ' = :userId')->bind(':userId', $value, ParameterType::INTEGER);
    // Set and query the database.
    return (bool) $db->setQuery($query)->loadResult();
}