private OffsetFetchResponse offsetFetchResponse(Errors error, Map<TopicPartition, PartitionData> responseData) {
        return new OffsetFetchResponse(throttleMs,
                                       singletonMap(groupId, error),
                                       singletonMap(groupId, responseData));
    }
Verifies that subscription change updates SubscriptionState correctly even after JoinGroup failures
that don't re-invoke onJoinPrepare.
clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinatorTest.java