How to unit test Spring Cloud Stream with Kafka DSL

Question

I am trying to (unit) test a Spring Cloud Stream Kafka processor that uses Kafka DSL, but receives the following error "Connection to node -1 could not be established. Broker may not be available.". Besides, the test does not shut down. I tried both EmbeddedKafka and TestBinder and yet I have the same behavior. I tried to start from the reponse given by Spring Cloud Team (which works) and I adapted the application to use Kafka DSL and left the test class pretty much as is. Does EmbeddedKafka actually support Kafka DSL?

I am using Elmhurst.RELEASE

@SpringBootApplication
@EnableBinding(MyBinding.class)
public class So43330544Application {

    public static void main(String[] args) {
        SpringApplication.run(So43330544Application.class, args);
    }

    @StreamListener
    @SendTo(MyBinding.OUTPUT)
    public KStream<String,String> process(@Input(MyBinding.INPUT) KStream<String, String> in) {

        return in.peek((k,v) -> System.out.println("Received value " +v ))
                .mapValues(v -> v.toUpperCase());
    }
}

interface MyBinding {

    String INPUT = "input";
    String OUTPUT = "output";

    @Input(INPUT)
    KStream<String, String> messagesIn();

    @Output(OUTPUT)
    KStream<String, String> messagesOut();
} 

---

Update

As shown in the following example, the approach proposed in this answer worked for me when I am using the Spring Cloud Stream generic syntax for writing event processors, but did not work when I am using Kafka DSL (KStreams). To see the difference in behaviors, just switch to either ExampleAppWorking or ExampleAppNotWorking in the @SpringBootTest annotation :

@RunWith(SpringRunner.class)
@SpringBootTest(classes=ExampleKafkaEmbeddedTest.ExampleAppNotWorking.class)
@DirtiesContext(classMode=ClassMode.AFTER_EACH_TEST_METHOD)
public class ExampleKafkaEmbeddedTest {
    @ClassRule
    public static KafkaEmbedded embeddedKafka = new KafkaEmbedded(1, false, "so0544in","so0544out");

    @Autowired
    private KafkaTemplate<Integer, byte[]> template;

    @Autowired
    private KafkaProperties properties;

    private static Consumer consumer;

    @BeforeClass
    public static void setup() throws Exception{
        System.setProperty("spring.kafka.bootstrap-servers", embeddedKafka.getBrokersAsString());
        System.setProperty("spring.cloud.stream.kafka.binder.zkNodes", embeddedKafka.getZookeeperConnectionString());
        System.setProperty("server.port","0");
        System.setProperty("spring.jmx.enabled" , "false");

        Map<String, Object> consumerProps = KafkaTestUtils.consumerProps("group-id", "false", embeddedKafka);

        consumerProps.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        consumerProps.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        DefaultKafkaConsumerFactory<String, String> cf = new DefaultKafkaConsumerFactory<>(consumerProps);
        consumer = cf.createConsumer();
        embeddedKafka.consumeFromAnEmbeddedTopic(consumer, "so0544out");

    }

    @After
    public void tearDown() {
        if (consumer != null){
            consumer.close();
        }
    }

    @Test
    public void testSendReceive() {
        template.send("so0544in", "foo".getBytes());

        Map<String, Object> configs = properties.buildConsumerProperties();
        configs.put(ConsumerConfig.GROUP_ID_CONFIG, "test0544");
        configs.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

        ConsumerRecord<String, String> cr = KafkaTestUtils.getSingleRecord(consumer, "so0544out");

        System.out.println("Contenu chaine resultat : " + cr.value());

        assertEquals(cr.value(), "FOO");
    }

    @SpringBootApplication
    @EnableBinding(Processor.class)
    public static class ExampleAppWorking {

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

        @StreamListener(Processor.INPUT)
        @SendTo(Processor.OUTPUT)
        public String receive(String in) {
            return in.toUpperCase();
        }
    }

    @SpringBootApplication
    @EnableBinding(MyBinding.class)
    public static class ExampleAppNotWorking {

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

        @StreamListener
        @SendTo(MyBinding.OUTPUT)
        public KStream<Integer,byte[]> toUpperCase (@Input(MyBinding.INPUT) KStream<Integer,byte[]> in){
            return in.map((key, val) -> KeyValue.pair(key, new String(val).toUpperCase().getBytes()));
        }
    }

    public interface MyBinding {
        String INPUT = "input";
        String OUTPUT = "output";

        @Input(INPUT)
        KStream<Integer, String> messagesIn();

        @Input(OUTPUT)
        KStream<Integer, String> messagesOut();
    }

}

Answer 1

EmbeddedKafa should work with Kafka Streams. All these tests use EmbeddedKafa for testing. You can follow the patterns used in these tests as a template for your own testing.

Looked at the code you provided below in the comments. You need to add this property in your setup method.

System.setProperty("spring.cloud.stream.kafka.streams.binder.brokers", embeddedKafka.getBrokersAsString());

The main Spring Boot application expects that the Kafka broker is available at localhost and it doesn't know that the test is running an embedded broker. We need to make that fact explicit by setting that property from the test so that the main boot application correctly detect the embedded kafka broker.