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Kafka Unit Testing


Allows you to start and stop a Kafka broker + ZooKeeper instance for unit testing applications that communicate with Kafka.


kafka-unit Kafka broker Zookeeper
1.0 kafka_2.11: 3.4.10
0.7 kafka_2.11: 3.4.10
0.6 kafka_2.11: 3.4.6
0.5 kafka_2.11: 3.4.6
0.4 kafka_2.11: 3.4.6
0.3 kafka_2.11: 3.4.6
0.2 kafka_2.11: 3.4.6

Maven central


Starting manually

To start both a Kafka server and ZooKeeper instance on random ports use following code:

KafkaUnit kafkaUnitServer = new KafkaUnit();

ZooKeeper and Kafka broker ports can be specified explicitly using second constructor, which takes two ints:

KafkaUnit kafkaUnitServer = new KafkaUnit(5000, 5001);

The alternative constructor allows providing connection strings rather than ports, which might be convenient if you want to use existing config without parsing it to extract port numbers:

KafkaUnit kafkaUnitServer = new KafkaUnit("localhost:5000", "localhost:5001");

Currently only localhost is supported and it's required that the connection string consists of only one localhost:[port] pair.

You can then write your own code to interact with Kafka or use the following methods:

ProducerRecord<String, String> keyedMessage = new ProducerRecord<>(testTopic, "key", "value");

And to read messages:

List<String> messages = kafkaUnitServer.readMessages(testTopic, 1);
List<String> allMessages = kafkaUnitServer.readAllMessages(testTopic);

Only String messages are supported at the moment.

Alternatively, you can use getKafkaConnect() to manually configure producer and consumer clients like:

Properties props = new Properties();
props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, LongSerializer.class.getCanonicalName());
props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getCanonicalName());
props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaUnitServer.getKafkaConnect());

Producer<Long, String> producer = new KafkaProducer<>(props);

Using the JUnit Rule

If you don't want to start/stop the server manually, you can use the JUnit rule, e.g.

public class KafkaUnitIntegrationTest {

    public KafkaUnitRule kafkaUnitRule = new KafkaUnitRule();

    public void junitRuleShouldHaveStartedKafka() throws Exception {
        String testTopic = "TestTopic";
        ProducerRecord<String, String> keyedMessage = new ProducerRecord<>(testTopic, "key", "value");

        List<String> messages = kafkaUnitRule.getKafkaUnit().readMessages(testTopic, 1);

        assertEquals(Arrays.asList("value"), messages);

This will start/stop the broker every test, so that particular test can't interfere with the next. Contrary to KafkaUnit() constructor, it does not throw checked IOException when socket initialization fails, but wraps it in runtime exception and thus is suitable for use as @Rule field in tests.

If you want to start server on specific ports, use KafkaUnitRule(int, int) or KafkaUnitRule(String, String) constructor, which accepts ZooKeeper and Kafka broker ports or connection strings respectively (just like corresponding KafkaUnit constructors), e.g.:

    public KafkaUnitRule kafkaUnitRule = new KafkaUnitRule(5000, 5001);


Copyright 2013 Christopher Batey

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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