drupal/modules/simpletest/tests/session_test.module

<?php
// $Id$

/**
 * Implementation of hook_menu().
 */
function session_test_menu() {
  $items['session-test/get'] = array(
    'title' => t('Session value'),
    'page callback' => '_session_test_get',
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
  );
  $items['session-test/set/%'] = array(
    'title' => t('Set Session value'),
    'page callback' => '_session_test_set',
    'page arguments' => array(2),
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
  );
  $items['session-test/no-set/%'] = array(
    'title' => t('Disabled session set value'),
    'page callback' => '_session_test_no_set',
    'page arguments' => array(2),
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
  );

  return $items;
}

/**
 * Page callback, prints the stored session value to the screen.
 */
function _session_test_get() {
  return t('The current value of the stored session variable is: %val', array('%val' => $_SESSION['session_test_value']));
}

/**
 * Page callback, stores a value in $_SESSION['session_test_value'].
 */
function _session_test_set($value) {
  $_SESSION['session_test_value'] = $value;
  return t('The current value of the stored session variable has been set to %val', array('%val' => $value));
}

/**
 * Menu callback: turns off session saving and then tries to save a value
 * anyway.
 */
function _session_test_no_set($value) {
  drupal_save_session(FALSE);
  _session_test_set($value);
  return t('session saving was disabled, and then %val was set', array('%val' => $value));
}