assertEquals("Executed: null null", result);

        // Test with empty strings
        result = jobExecutor.execute("", "");
        assertEquals("Executed:  ", result);
    }

    public void test_addShutdownListener() {
        // Test adding shutdown listener
        AtomicBoolean shutdownCalled = new AtomicBoolean(false);
        ShutdownListener listener = new ShutdownListener() {
            @Override