KAFKA-14059 Replace PowerMock with Mockito in WorkerSourceTaskTest (#13383)

Reviewers: Chris Egerton <chrise@aiven.io>

build.gradle

@@ -419,8 +419,7 @@ subprojects {
       "**/DistributedHerderTest.*",
       "**/KafkaConfigBackingStoreTest.*",
       "**/KafkaBasedLogTest.*", "**/StandaloneHerderTest.*",
-      "**/WorkerSinkTaskTest.*", "**/WorkerSinkTaskThreadedTest.*",
-      "**/WorkerSourceTaskTest.*"
+      "**/WorkerSinkTaskTest.*", "**/WorkerSinkTaskThreadedTest.*"
     ])
   }
 

connect/runtime/src/main/java/org/apache/kafka/connect/runtime/WorkerSourceTask.java

@@ -58,7 +58,8 @@ class WorkerSourceTask extends AbstractWorkerSourceTask {
     private static final Logger log = LoggerFactory.getLogger(WorkerSourceTask.class);
 
     private volatile CommittableOffsets committableOffsets;
-    private final SubmittedRecords submittedRecords;
+    //VisibleForTesting
+    final SubmittedRecords submittedRecords;
     private final AtomicReference<Exception> producerSendException;
 
     public WorkerSourceTask(ConnectorTaskId id,
@@ -320,7 +321,8 @@ class WorkerSourceTask extends AbstractWorkerSourceTask {
         return true;
     }
 
-    private void updateCommittableOffsets() {
+    // Visible for testing
+    void updateCommittableOffsets() {
         CommittableOffsets newOffsets = submittedRecords.committableOffsets();
         synchronized (this) {
             this.committableOffsets = this.committableOffsets.updatedWith(newOffsets);