Dummy shutdown function which registers another shutdown function.
function _system_test_first_shutdown_function($arg1, $arg2) {
// Output something, page has already been printed and the session stored
// so we can't use drupal_set_message.
print t('First shutdown function, arg1 : @arg1, arg2: @arg2', array(
'@arg1' => $arg1,
'@arg2' => $arg2,
));
drupal_register_shutdown_function('_system_test_second_shutdown_function', $arg1, $arg2);
}