require_once 'includes/password.inc';
$uids = db_select('users', 'u')
->fields('u', array('uid'))
->execute()->fetchCol();
foreach($uids as $uid) {
$user = null;
if ($uid != 0) {
$user = user_load($uid);
$user->pass = user_hash_password('test');
user_save($user);
}
}