How to write Unit test for @KafkaListener?

Question

Trying to figure out if I can write unit test for @KafkaListener using spring-kafka and spring-kafka-test.

My Listener class.

    public class MyKafkaListener {
    @Autowired
    private MyMessageProcessor myMessageProcessor;

    @KafkaListener(topics = "${kafka.topic.01}", groupId = "SF.CLIENT", clientIdPrefix = "SF.01", containerFactory = "myMessageListenerContainerFactory")
    public void myMessageListener(MyMessage message) {
        myMessageProcessor.process(message);
        log.info("MyMessage processed");
    }}

My Test class :

    @RunWith(SpringRunner.class)
    @DirtiesContext
    @EmbeddedKafka(partitions = 1, topics = {"I1.Topic.json.001"})
    @ContextConfiguration(classes = {TestKafkaConfig.class})
    public class MyMessageConsumersTest {

    @Autowired
    private MyMessageProcessor myMessageProcessor;

    @Value("${kafka.topic.01}")
    private String TOPIC_01;

    @Autowired
    private KafkaTemplate<String, MyMessage> messageProducer;

    @Test
    public void testSalesforceMessageListner() {
        MyMessageConsumers myMessageConsumers = new MyMessageConsumers(mockService);
        messageProducer.send(TOPIC_01, "MessageID", new MyMessage());
        verify(myMessageProcessor, times(1)).process(any(MyMessage.class));
    }}

My Test config class :

    @Configuration
    @EnableKafka
    public class TestKafkaConfig {
    @Bean
    public MyMessageProcessor myMessageProcessor() {
        return mock(MyMessageProcessor.class);
    }
    @Bean
    public KafkaEmbedded kafkaEmbedded() {
        return new KafkaEmbedded(1, true, 1, "I1.Topic.json.001");
    }

    //Consumer
    @Bean
    public ConsumerFactory<String, MyMessage> myMessageConsumerFactory() {
        Map<String, Object> props = new HashMap<>();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaEmbedded().getBrokersAsString());
        props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, false);
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        return new DefaultKafkaConsumerFactory<>(props, new StringDeserializer(), new JsonDeserializer<>(MyMessage.class));
    }
    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, MyMessage> myMessageListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, MyMessage> factory = new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(myMessageConsumerFactory());
        return factory;
    }

    //Producer
    @Bean
    public ProducerFactory<String, MyMessage> producerFactory() {
        Map<String, Object> props = new HashMap<>();
        props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaEmbedded().getBrokersAsString());
        props.put(ProducerConfig.RETRIES_CONFIG, 0);
        props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
        props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, KafkaMessageSerializer.class);
        return new DefaultKafkaProducerFactory<>(props);
    }
    @Bean
    public KafkaTemplate<String, MyMessage> messageProducer() {
        return new KafkaTemplate<>(producerFactory());
    }
    }

Is there any simple way to make this work ?

Or should I do the testing of @KafkaListener in some other way ? In unit test, how do I ensure @KafkaListener is invoked when a new message is arrived in Kafka.

Answer 1

In unit test, how do I ensure @KafkaListener is invoked when a new message is arrived in Kafka.

Instead of using Awaitility or CountDownLatch approach , a more easy way is to make the actual @KafkaListener bean as the mockito spy using @SpyBean. Spy basically allows you to record all interactions made on an actual bean instance such that you can verify its interactions later. Together with the timeout verify feature of the mockito , you can ensure that the verification will be done over and over until certain timeout after the producer send out the message.

Something like :

@SpringBootTest(properties = {"spring.kafka.bootstrap-servers=${spring.embedded.kafka.brokers}"})
@EmbeddedKafka(topics = {"fooTopic"})
public class MyMessageConsumersTest {

   @SpyBean
   private MyKafkaListener myKafkaListener;

   @Captor
   private ArgumentCaptor<MyMessage> myMessageCaptor;

   @Test
   public void test(){

      //create KafkaTemplate to send some message to the topic...

       verify(myKafkaListener, timeout(5000)). myMessageListener(myMessageCaptor.capture());
       
      //assert the KafkaListener is configured correctly such that it is invoked with the expected parameter
       assertThat(myMessageCaptor.getValue()).isEqualTo(xxxxx);
      
   }

Answer 2

If you want to write integration tests using EmbeddedKafka, then you can do something like this. Assume we have some KafkaListener, which accepts a RequestDto as a Payload.

In your test class you should create a TestConfiguration in order to create producer beans and to autowire KafkaTemplate into your test. Also notice, that instead of autowiring consumer, we inject a consumer SpyBean.

In someTest method we are creating a latch, and setting up the consumer listener method so that when it is called, the latch will be opened and assertions will take place only after the listener have received the Payload.

Also notice any() ?: RequestDto() line. You should use elvis operator with any() only if you are using Mockito's any() with non-null Kotlin method arguments, because any() firstly returns null.

@EnableKafka
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
@EmbeddedKafka(partitions = 10, brokerProperties = ["listeners=PLAINTEXT://localhost:9092", "port=9092"])
class KafkaIgniteApplicationTests {

    @SpyBean
    private lateinit var consumer: Consumer

    @TestConfiguration
    class Config {

        @Value("\${spring.kafka.consumer.bootstrap-servers}")
        private lateinit var servers: String

        fun producerConfig(): Map<String, Any> {
            val props = mutableMapOf<String, Any>()
            props[ProducerConfig.BOOTSTRAP_SERVERS_CONFIG] = servers
            props[ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG] = StringSerializer::class.java
            props[ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG] = StringSerializer::class.java
            return props
        }

        @Bean
        fun producerFactory(): ProducerFactory<String, String> {
            return DefaultKafkaProducerFactory(producerConfig())
        }

        @Bean
        fun kafkaTemplate(producerFactory: ProducerFactory<String, String>): KafkaTemplate<String, String> {
            return KafkaTemplate(producerFactory)
        }
    }

    @Autowired
    private lateinit var kafkaTemplate: KafkaTemplate<String, String>

    @Test
    fun someTest() {
        val lock = CountDownLatch(1)
        `when`(consumer.receive(any() ?: RequestDto())).thenAnswer {
            it.callRealMethod()
            lock.countDown()
        }
        val request = "{\"value\":\"1\"}"
        kafkaTemplate.send(TOPIC, request)
        lock.await(1000, TimeUnit.MILLISECONDS)
        verify(consumer).receive(RequestDto().apply { value = BigDecimal.ONE })
    }
}

Answer 3

Here is my working solution for the Consumer, based on your code. Thank you :-)

The Configuration is the following:

@TestConfiguration
@EnableKafka
@Profile("kafka_test")
public class KafkaTestConfig {

    private static Logger log = LoggerFactory.getLogger(KafkaTestConfig.class);

    @Value("${spring.kafka.bootstrap-servers}")
    private String bootstrapServers;

    @Bean
    @Primary
    public Map<String, Object> consumerConfigs() {
        Map<String, Object> props = new HashMap<>();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServers);
        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, JsonDeserializer.class);
        props.put(ConsumerConfig.GROUP_ID_CONFIG, "group-id");
        props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, false);
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        props.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, 15000);

        log.info("Consumer TEST config = {}", props);
        return props;
    }

    @Bean
    public Map<String, Object> producerConfigs() {
        Map<String, Object> props = new HashMap<>();
        props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServers);
        props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
        props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, JsonSerializer.class);

        log.info("Producer TEST config = {}", props);
        return props;
    }

    @Bean
    public ConsumerFactory<String, String> consumerFactory() {
        return new DefaultKafkaConsumerFactory<>(consumerConfigs(), new StringDeserializer(),
                new JsonDeserializer<String>());
    }

    @Bean
    public ProducerFactory<String, String> producerFactory() {
        DefaultKafkaProducerFactory<String, String> pf = new DefaultKafkaProducerFactory<>(producerConfigs());
        return pf;
    }

    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory(
            ConsumerFactory<String, String> kafkaConsumerFactory) {
        ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        factory.getContainerProperties().setAckOnError(false);
        factory.setConcurrency(2);
        return factory;
    }

    @Bean
    public KafkaTemplate<String, String> kafkaTemplate() {
        KafkaTemplate<String, String> kafkaTemplate = new KafkaTemplate<>(producerFactory());
        return kafkaTemplate;
    }

    @Bean
    public KafkaListenerEndpointRegistry kafkaListenerEndpointRegistry() {
        KafkaListenerEndpointRegistry kafkaListenerEndpointRegistry = new KafkaListenerEndpointRegistry();
        return kafkaListenerEndpointRegistry;
    }
}

Place all the beans you need to include in the test in a different class:

@TestConfiguration
@Profile("kafka_test")
@EnableKafka
public class KafkaBeansConfig {

    @Bean
    public MyProducer myProducer() {
        return new MyProducer();
    }

    // more beans
}

I created a BaseKafkaConsumerTest class to reuse it :

@ExtendWith(SpringExtension.class)
@TestPropertySource(properties = { "spring.kafka.bootstrap-servers=${spring.embedded.kafka.brokers}" })
@TestInstance(Lifecycle.PER_CLASS)
@DirtiesContext
@ContextConfiguration(classes = KafkaTestConfig.class)
@ActiveProfiles("kafka_test")
public class BaseKafkaConsumerTest {

    @Autowired
    protected EmbeddedKafkaBroker embeddedKafka;

    @Value("${spring.embedded.kafka.brokers}")
    private String brokerAddresses;

    @Autowired
    protected KafkaListenerEndpointRegistry kafkaListenerEndpointRegistry;

    @Autowired
    protected KafkaTemplate<String, String> senderTemplate;

    public void setUp() {
        embeddedKafka.brokerProperty("controlled.shutdown.enable", true);

        for (MessageListenerContainer messageListenerContainer : kafkaListenerEndpointRegistry
                .getListenerContainers()) {
            System.err.println(messageListenerContainer.getContainerProperties().toString());
            ContainerTestUtils.waitForAssignment(messageListenerContainer, embeddedKafka.getPartitionsPerTopic());
        }
    }

    @AfterAll
    public void tearDown() {
        for (MessageListenerContainer messageListenerContainer : kafkaListenerEndpointRegistry
                .getListenerContainers()) {
            messageListenerContainer.stop();
        }

        embeddedKafka.getKafkaServers().forEach(b -> b.shutdown());
        embeddedKafka.getKafkaServers().forEach(b -> b.awaitShutdown());
    }

}

Extend the base class to stest your consumer:

@EmbeddedKafka(topics = MyConsumer.TOPIC_NAME)
@Import(KafkaBeansConfig.class)
public class MYKafkaConsumerTest extends BaseKafkaConsumerTest {

    private static Logger log = LoggerFactory.getLogger(PaymentMethodsKafkaConsumerTest.class);

    @Autowired
    private MyConsumer myConsumer;

    // mocks with @MockBean

    @Configuration
    @ComponentScan({ "com.myfirm.kafka" })
    static class KafkaLocalTestConfig {
    }

    @BeforeAll
    public void setUp() {
        super.setUp();
    }

    @Test
    public void testMessageIsReceived() throws Exception {

    //mocks

    String jsonPayload = "{\"id\":\"12345\","cookieDomain\":"helloworld"}";
    ListenableFuture<SendResult<String, String>> future =
        senderTemplate.send(MyConsumer.TOPIC_NAME, jsonPayload);

    Thread.sleep(10000);
    future.addCallback(new ListenableFutureCallback<SendResult<String, String>>() {

        @Override
        public void onSuccess(SendResult<String, String> result) {
            log.info("successfully sent message='{}' with offset={}", jsonPayload,
                result.getRecordMetadata().offset());
        }

        @Override
        public void onFailure(Throwable ex) {
            log.error("unable to send message='{}'", jsonPayload, ex);
        }
    });

    Mockito.verify(myService, Mockito.times(1))
    .update(Mockito.any(MyDetails.class));
}

As I read in other posts, don´t test the business logic this way. Just that the calls are made.

Answer 4

You can wrap the listener in your test case.

Given

@SpringBootApplication
public class So52783066Application {

    public static void main(String[] args) {
        SpringApplication.run(So52783066Application.class, args);
    }

    @KafkaListener(id = "so52783066", topics = "so52783066")
    public void listen(String in) {
        System.out.println(in);
    }

}

then

@RunWith(SpringRunner.class)
@SpringBootTest
public class So52783066ApplicationTests {

    @ClassRule
    public static KafkaEmbedded embeddedKafka = new KafkaEmbedded(1, true, "so52783066");

    @Autowired
    private KafkaListenerEndpointRegistry registry;

    @Autowired
    private KafkaTemplate<String, String> template;

    @Before
    public void setup() {
        System.setProperty("spring.kafka.bootstrap-servers", embeddedKafka.getBrokersAsString());
    }

    @Test
    public void test() throws Exception {
        ConcurrentMessageListenerContainer<?, ?> container = (ConcurrentMessageListenerContainer<?, ?>) registry
                .getListenerContainer("so52783066");
        container.stop();
        @SuppressWarnings("unchecked")
        AcknowledgingConsumerAwareMessageListener<String, String> messageListener = (AcknowledgingConsumerAwareMessageListener<String, String>) container
                .getContainerProperties().getMessageListener();
        CountDownLatch latch = new CountDownLatch(1);
        container.getContainerProperties()
                .setMessageListener(new AcknowledgingConsumerAwareMessageListener<String, String>() {

                    @Override
                    public void onMessage(ConsumerRecord<String, String> data, Acknowledgment acknowledgment,
                            Consumer<?, ?> consumer) {
                        messageListener.onMessage(data, acknowledgment, consumer);
                        latch.countDown();
                    }

                });
        container.start();
        template.send("so52783066", "foo");
        assertThat(latch.await(10, TimeUnit.SECONDS)).isTrue();
    }

}

Answer 5

how do I ensure @KafkaListener is invoked when a new message is arrived in Kafka.

Well, this is essentially a Framework responsibility to test such a functionality. In your case you need just concentrate on the business logic and unit test exactly your custom code, but not that one compiled in the Framework. In addition there is not goo point to test the @KafkaListener method which just logs incoming messages. It is definitely going to be too hard to find the hook for test-case verification.

On the other hand I really believe that business logic in your @KafkaListener method is much complicated than you show. So, it might be really better to verify your custom code (e.g. DB insert, some other service call etc.) called from that method rather than try to figure out the hook exactly for the myMessageListener().

What you do with the mock(MyMessageProcessor.class) is really a good way for business logic verification. Only what is wrong in your code is about that duplication for the EmbeddedKafka: you use an annotation and you also declare a @Bean in the config. You should think about removing one of them. Although it isn't clear where is your production code, which is really free from the embedded Kafka. Otherwise, if everything is in the test scope, I don't see any problems with your consumer and producer factories configuration. You definitely have a minimal possible config for the @KafkaListener and KafkaTemplate. Only what you need is to remove a @EmbeddedKafka do not start the broker twice.