code: func newMockEncodeDataFunc(mockStore *mock.NodeStore) func(chunk Chunk) []byte {
  	return func(chunk Chunk) []byte {
  		if err := mockStore.Put(chunk.Address(), encodeData(chunk)); err != nil {
  			log.Error(fmt.Sprintf("%T: Chunk %v put: %v", mockStore, chunk.Address().Log(), err))
  		}
  		return chunk.Address()[:]
  	}
  }
docs: // newMockEncodeDataFunc returns a function that stores the chunk data
  // to a mock store to bypass the default functionality encodeData.
  // The constructed function always returns the nil data, as DbStore does
  // not need to store the data, but still need to create the index.