Integration testing in multi module Maven project with Spring

Question

I have a multi module maven project with several modules (parent, service, updater1, updater2). The @SpringBootApplication is in 'service' module and the others doesn't have artifacts.

'updater1' is a module which have a Kafka listener and a http client, and when receives a kafka event launches a request to an external API. I want to create integration tests in this module with testcontainers , so I've created the containers and a Kafka producer to send a KafkaTemplate to my consumer.

My problem is the Kafka producer is autowiring to null, so the tests throws a NullPointerException. I think it should be a Spring configuration problem, but I can't find the problem. Can you help me? Thank's!

This is my test class:

@ExtendWith(SpringExtension.class)
@ContextConfiguration(classes = {KafkaConfiguration.class, CacheConfiguration.class, ClientConfiguration.class})
public class InvoicingTest {

@ClassRule
public static final Containers containers = Containers.Builder.aContainer()
        .withKafka()
        .withServer()
        .build();

private final MockHttpClient mockHttpClient =
        new MockHttpClient(containers.getHost(SERVER),
                containers.getPort(SERVER));

@Autowired
private KafkaEventProducer kafkaEventProducer;

@BeforeEach
@Transactional
void setUp() {
    mockHttpClient.reset();
}

@Test
public void createElementSuccesfullResponse() throws ExecutionException, InterruptedException, TimeoutException {

    mockHttpClient.whenPost("/v1/endpoint")
            .respond(HttpStatusCode.OK_200);

    kafkaEventProducer.produce("src/test/resources/event/invoiceCreated.json");

    mockHttpClient.verify();

}

And this is the event producer:

@Component
public class KafkaEventProducer {

private final KafkaTemplate<String, String> kafkaTemplate;

private final String topic;

@Autowired
KafkaInvoicingEventProducer(KafkaTemplate<String, String> kafkaTemplate,
                            @Value("${kafka.topic.invoicing.name}") String topic){
    this.kafkaTemplate = kafkaTemplate;
    this.topic = topic;
}

public void produce(String event){
    kafkaTemplate.send(topic, event);
}

}

Answer 1

You haven't detailed how KafkaEventProducer is implemented (is it a @Component ?), neither your test class is annotated with @SpringBootTest and the runner @RunWith .

Check out this sample, using Apache KakfaProducer:

import org.apache.kafka.clients.producer.KafkaProducer;

public void sendRecord(String topic, String event) {
        try (KafkaProducer<String, byte[]> producer = new KafkaProducer<>(producerProps(bootstrapServers, false))) {
            send(producer, topic, event);
        } 
    }

where

public void send(KafkaProducer<String, byte[]> producer, String topic, String event) {
    try {
      ProducerRecord<String, byte[]> record = new ProducerRecord<>(topic, event.getBytes());
      producer.send(record).get();
    } catch (InterruptedException | ExecutionException e) {
        fail("Not expected exception: " + e.getMessage());
    }
}


protected Properties producerProps(String bootstrapServer, boolean transactional) {
        Properties producerProperties = new Properties();
        producerProperties.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServer);
        producerProperties.put(KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());
        producerProperties.put(VALUE_SERIALIZER_CLASS_CONFIG, ByteArraySerializer.class.getName());
        if (transactional) {
            producerProperties.put(TRANSACTIONAL_ID_CONFIG, "my-transactional-id");
        }
            
        return producerProperties;
    }

and bootstrapServers is taken from kafka container:

KafkaContainer kafka = new KafkaContainer();
kafka.start();
bootstrapServers = kafka.getBootstrapServers();