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https://github.com/jupiter-tools/spring-test-kafka

Tools for integration testing of Apache Kafka with SpringBoot applications
https://github.com/jupiter-tools/spring-test-kafka

kafka spring-boot spring-boot-test spring-framework spring-kafka test-containers testcontainers

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Tools for integration testing of Apache Kafka with SpringBoot applications

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:toc: preamble

# Spring Test Kafka

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Tools to write integration tests of Spring Framework with the Apache Kafka.

## Overview

image:./images/spring-test-kafka-containers.png[redis container scheme]

## How to write integration tests on Spring Boot with Apache Kafka

Add this library in dependencies:

[source,xml]
----

com.jupiter-tools
spring-test-kafka
0.2

----

Now, you can start Kafka in docker (TestContainers) by the using of `@KafkaTestContainer` annotation in tests:

[source, java]
----
@SpringBootTest
@KafkaTestContainer
class RedisTestContainerTest {

@Autowired
private KafkaTemplate kafkaTemplate;

@Test
void sendAndReceiveTest() throws InterruptedException {
assertThat(kafkaTemplate).isNotNull();
kafkaTemplate.send("test-topic", "flight of a dragon");
...
}
}
----

You can use this annotation to start Kafka container in tests both with JUnit5 and JUnit4.
The implementation doesn't depend on some test framework, just on the Spring Framework.

## How to use multiple Kafka containers in the one test case:

[source, java]
----
@SpringBootTest
@KafkaTestContainer <1>
@KafkaTestContainer(bootstrapServersPropertyName = "second.kafka.server") <2>
class MultipleContainerInOneTest {

...

}
----
<1> start a first Kafka test container and set a bootstrap servers of started container to default Spring Boot properties (`spring.kafka.bootstrap-servers`)
<2> start one more Kafka container and set a bootstrap servers to specified property, exactly in this property you can read an actual value of bootstrap servers after run the application context.

## A better way to test your data in integration tests

You can test received messages after test execution if you use JSON format.
Just describe expected dataset for a test case by the using `@ExpectedDataSet` annotation:

[source, java]
----
@SpringBootTest
@KafkaTestContainer
@EnableKafkaTest(topics = {"test-topic", "another-topic"})
class ExpectedMessagesTest {

@Autowired
private KafkaTemplate kafkaTemplate;

@Test
@ExpectedMessages(topic = "test-topic", datasetFile = "/datasets/expected_event.json")
void firstTopic() {
kafkaTemplate.send("test-topic", new Foo("qwert"));
kafkaTemplate.send("test-topic", new Bar("baaark"));
}

@Test
@ExpectedMessages(topic = "another-topic", datasetFile = "/datasets/expected_another_event.json")
void anotherTopic() {
kafkaTemplate.send("another-topic", Bar.builder().time(new Date()).build());
}
}

class Foo {
String value;
}

class Bar {
String name;
Date time;
}
----

And after test execution, we will wait for messages declared in this JSON file.
The content of JSON dataset file:

[source, json]
----
{
"com.kafkatest.example.events.Foo": [
{
"value": "qwert"
}
],
"com.kafkatest.example.events.Bar": [
{
"name": "baaark"
}
]
}
----

Also, you can use `@NoMessagesExpected` to check the silence on air.
Receiving any messages will fail the test case.

[source, java]
----
@Test
@NoMessagesExpected(timeout = 3000)
void silence() {

}
----
Waits during the timeout for messages in Kafka topics(set in `@EnableKafkaTest`),
if receive something then throws an exception.