drupal/modules/locale/tests/locale_test.module

<?php
// $Id$

/**
 * @file
 * Mock module for locale layer tests.
 */

/**
 * Implement hook_locale().
 */
function locale_test_locale($op = 'groups') {
  switch ($op) {
    case 'groups':
      return array('custom' => t('Custom'));
  }
}

/**
 * For testing domain language negotiation, we fake it by setting
 * the HTTP_HOST here
 */
function locale_test_boot() {
  if (variable_get('locale_test_domain')) {
    $_SERVER['HTTP_HOST'] = variable_get('locale_test_domain');
  }
}