### Question:
BackgroundHiveSplitLoader implements HiveSplitLoader { @VisibleForTesting static void validateFileBuckets(ListMultimap<Integer, LocatedFileStatus> bucketFiles, int partitionBucketCount, String tableName, String partitionName) { if (bucketFiles.isEmpty()) { return; } int highestBucketNumber = max(bucketFiles.keySet()); if (highestBucketNumber >= partitionBucketCount) { throw new PrestoException(HIVE_INVALID_BUCKET_FILES, format( "Hive table '%s' is corrupt. The highest bucket number in the directory (%s) exceeds the bucket number range " + "defined by the declared bucket count (%s) for partition: %s", tableName, highestBucketNumber, partitionBucketCount, partitionName)); } } BackgroundHiveSplitLoader(
            Table table,
            Iterable<HivePartitionMetadata> partitions,
            TupleDomain<? extends ColumnHandle> compactEffectivePredicate,
            DynamicFilter dynamicFilter,
            Duration dynamicFilteringProbeBlockingTimeout,
            TypeManager typeManager,
            Optional<BucketSplitInfo> tableBucketInfo,
            ConnectorSession session,
            HdfsEnvironment hdfsEnvironment,
            NamenodeStats namenodeStats,
            DirectoryLister directoryLister,
            Executor executor,
            int loaderConcurrency,
            boolean recursiveDirWalkerEnabled,
            boolean ignoreAbsentPartitions,
            Optional<ValidWriteIdList> validWriteIds); @Override void start(HiveSplitSource splitSource); @Override void stop(); static boolean hasAttemptId(String bucketFilename);  }### Answer:
@Test public void testValidateFileBuckets() { ListMultimap<Integer, LocatedFileStatus> bucketFiles = ArrayListMultimap.create(); bucketFiles.put(1, null); bucketFiles.put(3, null); bucketFiles.put(4, null); bucketFiles.put(6, null); bucketFiles.put(9, null); assertPrestoExceptionThrownBy(() -> BackgroundHiveSplitLoader.validateFileBuckets(bucketFiles, 1, "tableName", "partitionName")) .hasErrorCode(HIVE_INVALID_BUCKET_FILES) .hasMessage("Hive table 'tableName' is corrupt. The highest bucket number in the directory (9) exceeds the bucket number range " + "defined by the declared bucket count (1) for partition: partitionName"); assertPrestoExceptionThrownBy(() -> BackgroundHiveSplitLoader.validateFileBuckets(bucketFiles, 5, "tableName", "partitionName")) .hasErrorCode(HIVE_INVALID_BUCKET_FILES) .hasMessage("Hive table 'tableName' is corrupt. The highest bucket number in the directory (9) exceeds the bucket number range " + "defined by the declared bucket count (5) for partition: partitionName"); assertPrestoExceptionThrownBy(() -> BackgroundHiveSplitLoader.validateFileBuckets(bucketFiles, 9, "tableName", "partitionName")) .hasErrorCode(HIVE_INVALID_BUCKET_FILES) .hasMessage("Hive table 'tableName' is corrupt. The highest bucket number in the directory (9) exceeds the bucket number range " + "defined by the declared bucket count (9) for partition: partitionName"); BackgroundHiveSplitLoader.validateFileBuckets(bucketFiles, 10, "tableName", "partitionName"); BackgroundHiveSplitLoader.validateFileBuckets(bucketFiles, 20, "tableName", "partitionName"); BackgroundHiveSplitLoader.validateFileBuckets(bucketFiles, 30, "tableName", "partitionName"); }