Test onFailure of spring-kafka sending message - spring-boot

Question

I try to test the onFailure case when I send a kafka message with producer but the onFailure method is never fire.
Here is my code where I send a message :
#Component
public class MessageSending {
#Autowired
Map<String, KafkaTemplate<String, String>> producerByCountry;
String topicName = "countryTopic";
public void sendMessage(String data) {
producerByCountry.get("countryName").send(topicName, data).addCallback(
onSuccess -> {},
onFailure -> log.error("failed")
);
}
}
Here is the test class but it's still a success case and I have no idea how I can test the failure case (I want to add some processing inside the onFailure block but I would like to first know how I can trigger onFailure by testing).
#EmbeddedKafka
#SpringBootTest
public class MessageSendingTest {
#MockBean
Map<Country, KafkaTemplate<String, String>> producerByCountry;
#Autowired
EmbeddedKafkaBroker embeddedKafka;
#Autowired
MessageSending messageSending;
#Test
void failTest(CapturedOutput capturedOutput) {
var props = KafkaTestUtils.producerProps(embeddedKafka);
var producerTemplate = new DefaultKafkaProducerFactory<String, String>(props);
var template = new KafkaTemplate<>(producerTemplate);
given(producerByCountry.get("USA"))).willReturn(template);
messageSending.sendMessage("data");
assertThat(capturedOutput).contains("failed");
}
}
I also tried the idea of this topic How to test Kafka OnFailure callback with Junit? by doing
doAnswer(invocationOnMock -> {
ListenableFutureCallback<SendResult<String, String>> listenableFutureCallback = invocationOnMock.getArgument(0);
KafkaProducerException value = new KafkaProducerException(new ProducerRecord<String, String>("myTopic", "myMessage"), "error", ex);
listenableFutureCallback.onFailure(value);
return null;
}).when(mock(ListenableFuture.class)).addCallback(any(ListenableFutureCallback.class));
But I got this mockito exception org.mockito.exceptions.misusing.UnnecessaryStubbingException due by when().addCallback
Can someone can help ?
Thanks.

Answer 1

You can use a mock template; see this answer for an example:
How to mock result from KafkaTemplate
EDIT
You can also mock the underlying Producer object - here is an example that is closer to your use case...
#SpringBootApplication
public class So75074961Application {
public static void main(String[] args) {
SpringApplication.run(So75074961Application.class, args);
}
#Bean
KafkaTemplate<String, String> france(ProducerFactory<String, String> pf) {
return new KafkaTemplate<>(pf, Map.of(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "france:9092"));
}
#Bean
KafkaTemplate<String, String> germany(ProducerFactory<String, String> pf) {
return new KafkaTemplate<>(pf, Map.of(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "germany:9092"));
}
}
#Component
class MessageSending {
private static final Logger log = LoggerFactory.getLogger(MessageSending.class);
#Autowired
Map<String, KafkaTemplate<String, String>> producerByCountry;
String topicName = "countryTopic";
public void sendMessage(String country, String data) {
producerByCountry.get(country).send(topicName, data).addCallback(
onSuccess -> log.info(onSuccess.getRecordMetadata().toString()),
onFailure -> log.error("failed: " + onFailure.getMessage()));
}
}
#SpringBootTest
#ExtendWith(OutputCaptureExtension.class)
class So75074961ApplicationTests {
#Test
void test(#Autowired MessageSending sending, CapturedOutput capture) {
ProducerFactory<String, String> pf = mock(ProducerFactory.class);
Producer<String, String> prod = mock(Producer.class);
given(pf.createProducer()).willReturn(prod);
willAnswer(inv -> {
Callback callback = inv.getArgument(1);
callback.onCompletion(null, new RuntimeException("test"));
return mock(Future.class);
}).given(prod).send(any(), any());
// inject the mock pf into "france" template
Map<?, ?> producers = KafkaTestUtils.getPropertyValue(sending, "producerByCountry", Map.class);
new DirectFieldAccessor(producers.get("france")).setPropertyValue("producerFactory", pf);
sending.sendMessage("france", "foo");
assertThat(capture)
.contains("failed: Failed to send; nested exception is java.lang.RuntimeException: test");
}
}
Use CompletableFuture instead of ListenableFuture for versions 3.0 or later.
public void sendMessage(String country, String data) {
producerByCountry.get(country).send(topicName, data).whenComplete(
(res, ex) -> {
if (ex == null) {
log.info(res.getRecordMetadata().toString());
}
else {
log.error("failed: " + ex.getMessage());
}
});
}
and
assertThat(capture)
.contains("failed: Failed to send");
(the latter because Spring Framework 6.0+ no longer merges nested exception messages; the top level exception is a KafkaProducerException, with the actual exception as its cause).