### Question:
StandbyTask extends AbstractTask { public List<ConsumerRecord<byte[], byte[]>> update(final TopicPartition partition, final List<ConsumerRecord<byte[], byte[]>> records) { log.debug("{} Updating standby replicas of its state store for partition [{}]", logPrefix, partition); return stateMgr.updateStandbyStates(partition, records); } StandbyTask(final TaskId id,
                final String applicationId,
                final Collection<TopicPartition> partitions,
                final ProcessorTopology topology,
                final Consumer<byte[], byte[]> consumer,
                final ChangelogReader changelogReader,
                final StreamsConfig config,
                final StreamsMetrics metrics,
                final StateDirectory stateDirectory); @Override void resume(); @Override void commit(); @Override void suspend(); @Override void close(final boolean clean); List<ConsumerRecord<byte[], byte[]>> update(final TopicPartition partition,
                                                       final List<ConsumerRecord<byte[], byte[]>> records);  }### Answer:
@SuppressWarnings("unchecked") @Test public void testUpdate() throws Exception { StreamsConfig config = createConfig(baseDir); StandbyTask task = new StandbyTask(taskId, applicationId, topicPartitions, topology, consumer, changelogReader, config, null, stateDirectory); restoreStateConsumer.assign(new ArrayList<>(task.checkpointedOffsets().keySet())); for (ConsumerRecord<Integer, Integer> record : Arrays.asList( new ConsumerRecord<>(partition2.topic(), partition2.partition(), 10, 0L, TimestampType.CREATE_TIME, 0L, 0, 0, 1, 100), new ConsumerRecord<>(partition2.topic(), partition2.partition(), 20, 0L, TimestampType.CREATE_TIME, 0L, 0, 0, 2, 100), new ConsumerRecord<>(partition2.topic(), partition2.partition(), 30, 0L, TimestampType.CREATE_TIME, 0L, 0, 0, 3, 100))) { restoreStateConsumer.bufferRecord(record); } for (Map.Entry<TopicPartition, Long> entry : task.checkpointedOffsets().entrySet()) { TopicPartition partition = entry.getKey(); long offset = entry.getValue(); if (offset >= 0) { restoreStateConsumer.seek(partition, offset); } else { restoreStateConsumer.seekToBeginning(singleton(partition)); } } task.update(partition2, restoreStateConsumer.poll(100).records(partition2)); StandbyContextImpl context = (StandbyContextImpl) task.context(); MockStateStoreSupplier.MockStateStore store1 = (MockStateStoreSupplier.MockStateStore) context.getStateMgr().getStore(storeName1); MockStateStoreSupplier.MockStateStore store2 = (MockStateStoreSupplier.MockStateStore) context.getStateMgr().getStore(storeName2); assertEquals(Collections.emptyList(), store1.keys); assertEquals(Utils.mkList(1, 2, 3), store2.keys); task.closeStateManager(true); File taskDir = stateDirectory.directoryForTask(taskId); OffsetCheckpoint checkpoint = new OffsetCheckpoint(new File(taskDir, ProcessorStateManager.CHECKPOINT_FILE_NAME)); Map<TopicPartition, Long> offsets = checkpoint.read(); assertEquals(1, offsets.size()); assertEquals(new Long(30L + 1L), offsets.get(partition2)); }