fail("Expected NullPointerException");
        } catch (NullPointerException e) {
            // Expected exception
            assertNotNull(e);
        }
    }

    public void test_shutdown_multipleCalls() {
        // Test multiple shutdown calls
        AtomicInteger shutdownCount = new AtomicInteger(0);
        jobExecutor.addShutdownListener(new ShutdownListener() {
            @Override