minor: Set Serdes for MockProducer for AK 2.7 partition fix KAFKA-10503 to fix new NPE

Since 2.7 Serdes are now used in the MockProducer’s #send method, which causes a
NPE with AK 2.7 if they’re not set.

Author: astubbs

parallel-consumer-core/src/test/java/io/confluent/parallelconsumer/ParallelEoSStreamProcessorTestBase.java

@@ -12,6 +12,7 @@
 import org.apache.kafka.clients.consumer.*;
 import org.apache.kafka.clients.producer.MockProducer;
 import org.apache.kafka.common.TopicPartition;
+import org.apache.kafka.common.serialization.Serdes;
 import org.junit.jupiter.api.BeforeEach;
 import pl.tlinkowski.unij.api.UniLists;
 import pl.tlinkowski.unij.api.UniMaps;
@@ -126,7 +127,8 @@ protected MockConsumer<String, String> setupClients() {
 
     protected void instantiateConsumerProducer() {
         LongPollingMockConsumer<String, String> consumer = new LongPollingMockConsumer<>(OffsetResetStrategy.EARLIEST);
-        MockProducer<String, String> producer = new MockProducer<>(true, null, null); // TODO do async testing
+        MockProducer<String, String> producer = new MockProducer<>(true,
+                Serdes.String().serializer(), Serdes.String().serializer()); // TODO do async testing
 
         this.producerSpy = spy(producer);
         this.consumerSpy = spy(consumer);

parallel-consumer-examples/parallel-consumer-example-core/src/test/java/io/confluent/parallelconsumer/examples/core/CoreAppTest.java

@@ -14,6 +14,8 @@
 import org.apache.kafka.clients.producer.MockProducer;
 import org.apache.kafka.clients.producer.Producer;
 import org.apache.kafka.common.TopicPartition;
+import org.apache.kafka.common.serialization.Serdes;
+import org.apache.kafka.common.serialization.Serializer;
 import org.awaitility.Awaitility;
 import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
@@ -81,7 +83,8 @@ Consumer<String, String> getKafkaConsumer() {
 
         @Override
         Producer<String, String> getKafkaProducer() {
-            return new MockProducer<>(true, null, null);
+            var stringSerializer = Serdes.String().serializer();
+            return new MockProducer<>(true, stringSerializer, stringSerializer);
         }
 
         @Override