function do_rollback($t)
{
    $pdo = Utils::setup();
    $tm = new TransactionManager($pdo);
    $tm->txn_begin();
    $pdo->query("INSERT INTO foo (id, var) VALUES (2, 'bal')");
    $tm->txn_rollback();
    $stmt = $row = $pdo->query('SELECT * FROM foo');
    $t->ok(!$stmt->fetch(PDO::FETCH_ASSOC));
}