performance-art.fr/modules/user/tests/user_session_test.module

<?php

/**
 * @file
 * Dummy module implementing a page callback to create an anon session.
 */

/**
 * Implements hook_menu().
 */
function user_session_test_menu() {
  $items = array();
  $items['user_session_test_anon_session'] = array(
    'page callback' => 'user_session_test_anon_session',
    'access callback' => TRUE,
  );
  return $items;
}

/**
 * Page callback.
 *
 * Creates an anonymous user session.
 */
function user_session_test_anon_session() {
  $data = 'This dummy data will be stored in a user session.';
  $_SESSION[__FUNCTION__] = $data;
  return $data;
}