Fix Race In Test

- use `BlockingQueue` instead of `ArrayList`.

Author: garyrussell

spring-kafka/src/test/java/org/springframework/kafka/listener/ConcurrentMessageListenerContainerTests.java

@@ -27,15 +27,16 @@
 import java.util.Arrays;
 import java.util.BitSet;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
+import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ConcurrentSkipListSet;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
@@ -151,7 +152,7 @@ protected Consumer<Integer, String> createKafkaConsumer(String groupId, String c
 				new ConcurrentMessageListenerContainer<>(cf, containerProps);
 		container.setConcurrency(2);
 		container.setBeanName("testAuto");
-		List<KafkaEvent> events = Collections.synchronizedList(new ArrayList<>());
+		BlockingQueue<KafkaEvent> events = new LinkedBlockingQueue<>();
 		CountDownLatch stopLatch = new CountDownLatch(4);
 		container.setApplicationEventPublisher(e -> {
 			events.add((KafkaEvent) e);