Can MockProducer and MockConsumer be used with kafkaTemplate producer - spring-boot

Question

I have a service which using kafkaTemplate to send the kafka message.
#Service
class KafkaProducer(#Autowired val kafkaTemplate: KafkaTemplate<String, String>) {
final fun sendMessage(msg: String) {
val abc = kafkaTemplate.send(AppConstants.TOPIC_NAME, "abc", msg)
abc.whenComplete {
result, ex ->
if (ex != null) {
print("ex occured")
print(ex.message)
} else {
print("sent successfully")
print(result.producerRecord.value())
}
}
}
}
For unit test, I am trying to mock this KafkaProducer.
Can i use MockProducer (import org.apache.kafka.clients.producer.MockProducer) for this?
#Test
fun verify_test() {
val mockProducer = MockProducer(true,StringSerializer(), StringSerializer())
val kafkaProducer = KafkaProducer(mockProducer)
}
On trying the above code, i am getting error bcoz KafkaProducer takes argument as KafkaTemplate object, and I am providing MockProducer.

Answer 1

Here is an example using a mock ProducerFactory...
#SpringJUnitConfig
class So74993413ApplicationTests {
#Test
void test(#Autowired KafkaTemplate<String, String> template,
#Autowired MockProducer<String, String> producer) throws Exception {
CompletableFuture<SendResult<String, String>> future = template.send("foo", "bar");
SendResult<String, String> sendResult = future.get();
// System.out.println(sendResult);
List<ProducerRecord<String, String>> history = producer.history();
assertThat(history).hasSize(1);
ProducerRecord<String, String> record = history.get(0);
assertThat(record.topic()).isEqualTo("foo");
assertThat(record.value()).isEqualTo("bar");
}
#Configuration
public static class Config {
#Bean
MockProducer<String, String> producer() {
return new MockProducer<>(true, new StringSerializer(), new StringSerializer());
}
#Bean
ProducerFactory<String, String> pf (MockProducer producer) {
return new ProducerFactory<>() {
#Override
public Producer<String, String> createProducer() {
return producer;
}
};
}
#Bean
KafkaTemplate<String, String> template(ProducerFactory<String, String> pf) {
return new KafkaTemplate<>(pf);
}
}
}

Answer 2

KafkaTemplate is not a type of Producer. Native Kafka classes cannot be used in place of Spring's - that'd be a reverse dependency.
You would have to mock the template instead since that's what you're actually using. By doing so, it'll bypass any KafkaProducer instance the template used, mock or not.