How to Mock a Kafka Consumer endpoint on a Camel Route?

Question

I have a Camel endpoint which is basically a Kafka Consumer reading from a topic and sending the information to a database. It is working fine, however, I am struggling to unit test it as I haven't been able to mock the Kafka endpoint. Can anyone help me in mocking a Kafka Consumer in a Camel Route?

@Override
public void configure() {    
    from(kafka:eph?brokers=localhost:9092...).routeId("KafkaConsumer")
        .to(direct:updateDatabase)
}

Answer 1

To unit test your route, you may do that with a standard camel spring boot test. During the test, the Kafka producer(in Camel's view) can be swapped in with a direct component and mock messages can be delivered there. To see if your routes are processing those messages properly, Mock endpoints can be used.

//Route definition
@Component
public class KafkaRoute extends RouteBuilder {

    public static final String KAFKA_ROUTE_NAME = "kafka-route";

    @Override
    public void configure() throws Exception {
        from("kafka:eph?brokers=localhost:9092").routeId(KAFKA_ROUTE_NAME)
                .log(LoggingLevel.INFO, "Message: ${body}  received on the topic: ${headers[kafka.TOPIC]} ")
                .to("direct:updateDatabase");

        from("direct:updateDatabase").log(LoggingLevel.INFO, "DB Updated.");

    }

}

import java.util.HashMap;
import java.util.Map;

import org.apache.camel.CamelContext;
import org.apache.camel.EndpointInject;
import org.apache.camel.Produce;
import org.apache.camel.ProducerTemplate;
import org.apache.camel.builder.AdviceWithRouteBuilder;
import org.apache.camel.component.kafka.KafkaConstants;
import org.apache.camel.component.mock.MockEndpoint;
import org.apache.camel.test.spring.CamelSpringBootRunner;
import org.apache.camel.test.spring.MockEndpoints;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.annotation.DirtiesContext;

@RunWith(CamelSpringBootRunner.class)
@SpringBootTest
@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
@MockEndpoints("direct:*")
public class KafkaRouteTest {

    @Autowired
    CamelContext camelContext;

    @Produce
    ProducerTemplate mockKafkaProducer;

    @EndpointInject("mock:direct:updateDatabase")
    MockEndpoint finalSink;

    @Test
    public void testKafkaRoute() throws Exception {

        //Here we swap the FROM component in the KafkaRoute.KAFKA_ROUTE_NAME with a direct component, direct:kafka-from
        AdviceWithRouteBuilder.adviceWith(camelContext, KafkaRoute.KAFKA_ROUTE_NAME, routeBuilder -> {
            routeBuilder.replaceFromWith("direct:kafka-from");
        });

        Map<String, Object> headers = new HashMap<>();
        headers.put(KafkaConstants.TOPIC, "testTopic");

        //Send mock message to the route
        mockKafkaProducer.sendBodyAndHeaders("direct:kafka-from", "test-body", headers);


        //Assertions. You may do additional assertions with the likes of Mockito
        finalSink.expectedBodiesReceived("test-body");
        finalSink.expectedHeaderReceived(KafkaConstants.TOPIC, "testTopic");
        finalSink.assertIsSatisfied();

    }

}

Camel Kafka component is already unit tested , there is no point in replicating all those tests in your code base. However, if you really want to do testing against a real Kafka instance, you may use test containers . Here is a full blown example, from the Camel repository itself, using test containers.

Answer 2

Simply externalize the endpoint URI in a property (for example with Spring Property facility)

from(consumerEndpoint).routeId("KafkaConsumer")

Then in your production configuration, you use the real endpoint

consumerEndpoint=kafka:eph?brokers=localhost:9092...

Whereas in your test configuration, you use a direct endpoint

consumerEndpoint=direct:consumer

This one is easy to trigger from a Camel route test

producer.sendBody("direct:consumer", myMessageBody);