code: def test_custom_hf_index_retriever_save_and_from_pretrained_from_disk(
      self,
  ):
      retriever = self.get_dummy_custom_hf_index_retriever(
          from_disk=True
      )
      with tempfile.TemporaryDirectory() as tmp_dirname:
          retriever.save_pretrained(tmp_dirname)
          retriever = RagRetriever.from_pretrained(tmp_dirname)
          self.assertIsInstance(retriever, RagRetriever)
          hidden_states = np.array(
              [
                  np.ones(self.retrieval_vector_size),
                  -np.ones(self.retrieval_vector_size),
              ],
              dtype=np.float32,
          )
          out = retriever.retrieve(hidden_states, n_docs=1)
          self.assertTrue(out is not None)
  
imports: import json
  import os
  import shutil
  import tempfile
  from unittest import TestCase
  from unittest.mock import patch
  import numpy
  from datasets import Dataset
  from transformers import is_faiss_available
  from transformers.models.bart.configuration_bart import BartConfig
  from transformers.models.bart.tokenization_bart import BartTokenizer
  from transformers.models.bert.tokenization_bert import VOCAB_FILES_NAMES
  from transformers.models.dpr.configuration_dpr import DPRConfig
  from transformers.models.dpr.tokenization_dpr import DPRContextEncoderTokenizer, DPRQuestionEncoderTokenizer
  from transformers.models.rag.configuration_rag import RagConfig
  from transformers.models.rag.retrieval_rag import CustomHFIndex, RagRetriever
  from transformers.models.roberta.tokenization_roberta import VOCAB_FILES_NAMES
  from transformers.testing_utils import require_faiss, require_sentencepiece, require_tokenizers, require_torch
label_desc: Use image node_id 14 for calling the RagRetrieverTest obj's underlying member method code with example usage: obj.test_custom_hf_index_retriever_save_and_from_pretrained_from_disk() without return types