boolean isTaskManagerRegistered(ResourceID taskManagerId) {
        return registeredTaskManagers.contains(taskManagerId);
    }
@Test
    void testUnknownTaskManagerRegistration() throws Exception {
        try (DeclarativeSlotPoolService declarativeSlotPoolService =
                createDeclarativeSlotPoolService()) {
            final ResourceID unknownTaskManager = ResourceID.generate();

            assertThat(
                            declarativeSlotPoolService.isTaskManagerRegistered(
                                    unknownTaskManager.getResourceID()))
                    .isFalse();
        }
    }