public String kafkaClusterId() {
        if (kafkaClusterId == null) {
            kafkaClusterId = lookupKafkaClusterId(this);
        }
        return kafkaClusterId;
    }
@Test
    public void testKafkaClusterId() {
        Map<String, String> props = baseProps();
        WorkerConfig config = new WorkerConfig(WorkerConfig.baseConfigDef(), props);
        assertEquals(CLUSTER_ID, config.kafkaClusterId());
        workerConfigMockedStatic.verify(() -> WorkerConfig.lookupKafkaClusterId(any(WorkerConfig.class)), times(1));

        // next calls hit the cache
        assertEquals(CLUSTER_ID, config.kafkaClusterId());
        workerConfigMockedStatic.verify(() -> WorkerConfig.lookupKafkaClusterId(any(WorkerConfig.class)), times(1));
    }