Removing slf4j-log4j12, deleting log4j.properties and adding a standard src/test/resources/logback.xml, since the Kafka libraries use the logback SLF4J binding.

apache-kafka-2/log4j.properties

@@ -1 +0,0 @@
-log4j.rootLogger=INFO, stdout

apache-kafka-2/pom.xml

@@ -23,11 +23,6 @@
             <artifactId>slf4j-api</artifactId>
             <version>${org.slf4j.version}</version>
         </dependency>
-        <dependency>
-            <groupId>org.slf4j</groupId>
-            <artifactId>slf4j-log4j12</artifactId>
-            <version>${org.slf4j.version}</version>
-        </dependency>
         <dependency>
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>

apache-kafka-2/src/test/java/com/baeldung/kafka/message/ordering/ExternalSequenceWithTimeWindowIntegrationTest.java

@@ -1,5 +1,6 @@
 package com.baeldung.kafka.message.ordering;
 
+import com.baeldung.kafka.headers.KafkaMessageHeaders;
 import com.baeldung.kafka.message.ordering.payload.UserEvent;
 import com.baeldung.kafka.message.ordering.serialization.JacksonDeserializer;
 import com.baeldung.kafka.message.ordering.serialization.JacksonSerializer;
@@ -16,6 +17,8 @@ import org.apache.kafka.common.serialization.LongSerializer;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.testcontainers.containers.KafkaContainer;
 import org.testcontainers.junit.jupiter.Container;
 import org.testcontainers.junit.jupiter.Testcontainers;
@@ -36,6 +39,8 @@ public class ExternalSequenceWithTimeWindowIntegrationTest {
     private static final Duration TIMEOUT_WAIT_FOR_MESSAGES = Duration.ofSeconds(5);
     private static final long BUFFER_PERIOD_NS = Duration.ofSeconds(5).toNanos();
 
+    private static Logger logger = LoggerFactory.getLogger(ExternalSequenceWithTimeWindowIntegrationTest.class);
+
     @Container
     private static final KafkaContainer KAFKA_CONTAINER = new KafkaContainer(DockerImageName.parse("confluentinc/cp-kafka:latest"));
 
@@ -80,7 +85,7 @@ public class ExternalSequenceWithTimeWindowIntegrationTest {
             Future<RecordMetadata> future = producer.send(new ProducerRecord<>(Config.MULTI_PARTITION_TOPIC, sequenceNumber, userEvent));
             sentUserEventList.add(userEvent);
             RecordMetadata metadata = future.get();
-            System.out.println("User Event ID: " + userEvent.getUserEventId() + ", Partition : " + metadata.partition());
+            logger.info("User Event ID: " + userEvent.getUserEventId() + ", Partition : " + metadata.partition());
         }
 
         consumer.subscribe(Collections.singletonList(Config.MULTI_PARTITION_TOPIC));
@@ -109,7 +114,7 @@ public class ExternalSequenceWithTimeWindowIntegrationTest {
         Collections.sort(buffer);
         buffer.forEach(userEvent -> {
             receivedUserEventList.add(userEvent);
-            System.out.println("Processing message with Global Sequence number: " + userEvent.getGlobalSequenceNumber() + ", User Event Id: " + userEvent.getUserEventId());
+            logger.info("Processing message with Global Sequence number: " + userEvent.getGlobalSequenceNumber() + ", User Event Id: " + userEvent.getUserEventId());
         });
         buffer.clear();
     }

apache-kafka-2/src/test/java/com/baeldung/kafka/message/ordering/MultiplePartitionIntegrationTest.java

@@ -16,6 +16,8 @@ import org.apache.kafka.common.serialization.LongSerializer;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.testcontainers.containers.KafkaContainer;
 import org.testcontainers.junit.jupiter.Container;
 import org.testcontainers.junit.jupiter.Testcontainers;
@@ -34,6 +36,8 @@ public class MultiplePartitionIntegrationTest {
     private static KafkaProducer<Long, UserEvent> producer;
     private static KafkaConsumer<Long, UserEvent> consumer;
     private static final Duration TIMEOUT_WAIT_FOR_MESSAGES = Duration.ofSeconds(5);
+
+    private static Logger logger = LoggerFactory.getLogger(MultiplePartitionIntegrationTest.class);
     @Container
     private static final KafkaContainer KAFKA_CONTAINER = new KafkaContainer(DockerImageName.parse("confluentinc/cp-kafka:latest"));
 
@@ -78,7 +82,7 @@ public class MultiplePartitionIntegrationTest {
             Future<RecordMetadata> future = producer.send(new ProducerRecord<>(Config.MULTI_PARTITION_TOPIC, sequenceNumber, userEvent));
             sentUserEventList.add(userEvent);
             RecordMetadata metadata = future.get();
-            System.out.println("User Event ID: " + userEvent.getUserEventId() + ", Partition : " + metadata.partition());
+            logger.info("User Event ID: " + userEvent.getUserEventId() + ", Partition : " + metadata.partition());
         }
 
         consumer.subscribe(Collections.singletonList(Config.MULTI_PARTITION_TOPIC));
@@ -86,7 +90,7 @@ public class MultiplePartitionIntegrationTest {
         records.forEach(record -> {
             UserEvent userEvent = record.value();
             receivedUserEventList.add(userEvent);
-            System.out.println("User Event ID: " + userEvent.getUserEventId());
+            logger.info("User Event ID: " + userEvent.getUserEventId());
         });
         assertThat(receivedUserEventList)
             .isNotEqualTo(sentUserEventList)

apache-kafka-2/src/test/java/com/baeldung/kafka/message/ordering/SinglePartitionIntegrationTest.java

@@ -18,6 +18,8 @@ import org.apache.kafka.common.serialization.LongSerializer;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.testcontainers.containers.KafkaContainer;
 import org.testcontainers.junit.jupiter.Container;
 import org.testcontainers.junit.jupiter.Testcontainers;
@@ -39,6 +41,7 @@ public class SinglePartitionIntegrationTest {
 
     private static final Duration TIMEOUT_WAIT_FOR_MESSAGES = Duration.ofSeconds(5);
 
+    private static Logger logger = LoggerFactory.getLogger(SinglePartitionIntegrationTest.class);
     @Container
     private static final KafkaContainer KAFKA_CONTAINER = new KafkaContainer(DockerImageName.parse("confluentinc/cp-kafka:latest"));
 
@@ -86,7 +89,7 @@ public class SinglePartitionIntegrationTest {
             Future<RecordMetadata> future = producer.send(producerRecord);
             sentUserEventList.add(userEvent);
             RecordMetadata metadata = future.get();
-            System.out.println("User Event ID: " + userEvent.getUserEventId() + ", Partition : " + metadata.partition());
+            logger.info("User Event ID: " + userEvent.getUserEventId() + ", Partition : " + metadata.partition());
         }
 
         consumer.subscribe(Collections.singletonList(Config.SINGLE_PARTITION_TOPIC));
@@ -94,7 +97,7 @@ public class SinglePartitionIntegrationTest {
         records.forEach(record -> {
             UserEvent userEvent = record.value();
             receivedUserEventList.add(userEvent);
-            System.out.println("User Event ID: " + userEvent.getUserEventId());
+            logger.info("User Event ID: " + userEvent.getUserEventId());
         });
         assertThat(receivedUserEventList)
             .isEqualTo(sentUserEventList)

apache-kafka-2/src/test/resources/logback.xml

@@ -0,0 +1,11 @@
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>