Kafka Streams Testing : java.util.NoSuchElementException: Uninitialized topic: "output_topic_name" - unit-testing

Question

I've written a test class for kafka stream application as per https://kafka.apache.org/24/documentation/streams/developer-guide/testing.html
, the code for which is
import com.EventSerde;
import org.apache.kafka.common.serialization.Serde;
import org.apache.kafka.common.serialization.Serdes;
import org.apache.kafka.streams.*;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.util.Properties;
public class KafkaStreamsConfigTest {
private TopologyTestDriver testDriver;
private TestInputTopic<String, Object> inputTopic;
private TestOutputTopic<String, Object> outputTopic;
private Serde<String> stringSerde = new Serdes.StringSerde();
private EventSerde eventSerde= new EventSerde();
private String key="test";
private Object value = "some value";
private Object expected_value = "real value";
String kafkaEventSourceTopic = "raw_events";
String kafkaEventSinkTopic = "processed_events";
String kafkaCacheSinkTopic = "cache_objects";
String applicationId = "my-app";
String test_dummy = "dummy:1234";
#Before
public void setup() {
Topology topology = new Topology();
topology.addSource(kafkaEventSourceTopic, kafkaEventSourceTopic);
topology.addProcessor(ProcessRouter.class.getSimpleName(), ProcessRouter::new, kafkaEventSourceTopic);
topology.addProcessor(WorkforceVisit.class.getSimpleName(), WorkforceVisit::new
, ProcessRouter.class.getSimpleName());
topology.addProcessor(DefaultProcessor.class.getSimpleName(), DefaultProcessor::new
, ProcessRouter.class.getSimpleName());
topology.addProcessor(CacheWorkforceShift.class.getSimpleName(), CacheWorkforceShift::new
, ProcessRouter.class.getSimpleName());
topology.addProcessor(DigitalcareShiftassisstantTracking.class.getSimpleName(), DigitalcareShiftassisstantTracking::new
, ProcessRouter.class.getSimpleName());
topology.addProcessor(WorkforceLocationUpdate.class.getSimpleName(), WorkforceLocationUpdate::new
, ProcessRouter.class.getSimpleName());
topology.addSink(kafkaEventSinkTopic, kafkaEventSinkTopic
, WorkforceVisit.class.getSimpleName(), DefaultProcessor.class.getSimpleName()
, CacheWorkforceShift.class.getSimpleName(), DigitalcareShiftassisstantTracking.class.getSimpleName()
, WorkforceLocationUpdate.class.getSimpleName());
topology.addSink(kafkaCacheSinkTopic, kafkaCacheSinkTopic
, WorkforceVisit.class.getSimpleName()
, CacheWorkforceShift.class.getSimpleName(), DigitalcareShiftassisstantTracking.class.getSimpleName()
, WorkforceLocationUpdate.class.getSimpleName());
Properties properties = new Properties();
properties.put(StreamsConfig.APPLICATION_ID_CONFIG, applicationId);
properties.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, test_dummy);
properties.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
properties.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, EventSerde.class.getName());
testDriver = new TopologyTestDriver(topology, properties);
//setup test topics
inputTopic = testDriver.createInputTopic(kafkaEventSourceTopic, stringSerde.serializer(), eventSerde.serializer());
outputTopic = testDriver.createOutputTopic(kafkaEventSinkTopic, stringSerde.deserializer(), eventSerde.deserializer());
}
#After
public void tearDown() {
testDriver.close();
}
#Test
public void outputEqualsTrue()
{
inputTopic.pipeInput(key, value);
Object b = outputTopic.readValue();
System.out.println(b.toString());
assertEquals(b,expected_value);
}
where I used EventSerde class to serialize and deserialize the value.
When I run this code it gives the error java.util.NoSuchElementException: Uninitialized topic: processed_events with the following stacktrace:
java.util.NoSuchElementException: Uninitialized topic: processed_events
at org.apache.kafka.streams.TopologyTestDriver.readRecord(TopologyTestDriver.java:715)
at org.apache.kafka.streams.TestOutputTopic.readRecord(TestOutputTopic.java:100)
at org.apache.kafka.streams.TestOutputTopic.readValue(TestOutputTopic.java:80)
at com.uhx.platform.eventprocessor.config.KafkaStreamsConfigTest.outputEqualsTrue(KafkaStreamsConfigTest.java:111)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
As you can see i have initialized both input and output topics.
I have also debugged the code and the error occurs when i read the value from output topic
outputTopic.readValue();
I don't understand what else i should do to initialize the outputTopic. Can anyone help me with this problem?
I am using apache kafka-streams-test-utils 2.4.0 and kafka-streams 2.4.0
<dependency>
<groupId>org.apache.kafka</groupId>
<artifactId>kafka-streams</artifactId>
<version>2.4.0</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.kafka/kafka-clients -->
<dependency>
<groupId>org.apache.kafka</groupId>
<artifactId>kafka-clients</artifactId>
<version>2.4.0</version>
</dependency>
<dependency>
<groupId>org.apache.kafka</groupId>
<artifactId>kafka-streams-test-utils</artifactId>
<version>2.4.0</version>
<scope>test</scope>
</dependency>

Answer 1

To avoid/overcome this exception, you need to check if your output topic is not empty before trying to read from it.
#Test
public void outputEqualsTrue()
{
inputTopic.pipeInput(key, value);
assert(outputTopic.isEmpty(), false);
Object b = outputTopic.readValue();
System.out.println(b.toString());
assertEquals(b,expected_value);
}