public void test_addShutdownListener_replacesExisting() {
        // Add first listener
        TestShutdownListener listener1 = new TestShutdownListener();
        scriptExecutor.addShutdownListener(listener1);

        // Add second listener (should replace first)
        TestShutdownListener listener2 = new TestShutdownListener();
        scriptExecutor.addShutdownListener(listener2);

        // Call shutdown