### Question:
PerformanceCachingGoogleCloudStorage extends ForwardingGoogleCloudStorage { @Override public void deleteBuckets(List<String> bucketNames) throws IOException { super.deleteBuckets(bucketNames); for (String bucket : bucketNames) { cache.invalidateBucket(bucket); } } PerformanceCachingGoogleCloudStorage(
      GoogleCloudStorage delegate, PerformanceCachingGoogleCloudStorageOptions options); @VisibleForTesting  PerformanceCachingGoogleCloudStorage(
      GoogleCloudStorage delegate,
      PrefixMappedItemCache cache); @Override WritableByteChannel create(StorageResourceId resourceId); @Override void deleteBuckets(List<String> bucketNames); @Override void deleteObjects(List<StorageResourceId> resourceIds); @Override List<GoogleCloudStorageItemInfo> listBucketInfo(); @Override List<String> listObjectNames(String bucketName, String objectNamePrefix); @Override List<String> listObjectNames(
      String bucketName, String objectNamePrefix, ListObjectOptions listOptions); @Override List<GoogleCloudStorageItemInfo> listObjectInfo(String bucketName, String objectNamePrefix); @Override List<GoogleCloudStorageItemInfo> listObjectInfo(
      String bucketName, String objectNamePrefix, ListObjectOptions listOptions); @Override ListPage<GoogleCloudStorageItemInfo> listObjectInfoPage(
      String bucketName, String objectNamePrefix, ListObjectOptions listOptions, String pageToken); @Override GoogleCloudStorageItemInfo getItemInfo(StorageResourceId resourceId); @Override List<GoogleCloudStorageItemInfo> getItemInfos(List<StorageResourceId> resourceIds); @Override List<GoogleCloudStorageItemInfo> updateItems(List<UpdatableItemInfo> itemInfoList); @Override void close(); @Override GoogleCloudStorageItemInfo composeObjects(
      List<StorageResourceId> sources, StorageResourceId destination, CreateObjectOptions options); @VisibleForTesting void invalidateCache();  }### Answer:
@Test public void testDeleteBuckets() throws IOException { List<String> buckets = Lists.newArrayList(BUCKET_A); cache.putItem(ITEM_A_A); cache.putItem(ITEM_B_A); gcs.deleteBuckets(buckets); verify(gcsDelegate).deleteBuckets(eq(buckets)); assertThat(cache.getAllItemsRaw()).containsExactly(ITEM_B_A); }