@Override
  protected KeyValueStore<byte[], byte[]> getKVStore(String storeName, File storeDir, MetricsRegistry registry,
      JobContext jobContext, ContainerContext containerContext, StoreMode storeMode) {
    return this.rawKeyValueStore;
  }
Used for testing {@link BaseKeyValueStorageEngineFactory}.
Implements {@link #getKVStore} to return a pre-built {@link KeyValueStore}.
samza-kv/src/test/java/org/apache/samza/storage/kv/MockKeyValueStorageEngineFactory.java