void testForceCleanup() {
        TestResource resource1 = new TestResource("cleanup1");
        TestResource resource2 = new TestResource("cleanup2");

        resourceManager.registerResource(resource1);
        resourceManager.registerResource(resource2);

        assertFalse(resource1.isClosed());
        assertFalse(resource2.isClosed());

        int cleaned = resourceManager.forceCleanup();