code: def test_canonical_hf_index_retriever_save_and_from_pretrained(self):
      retriever = self.get_dummy_canonical_hf_index_retriever()
      with tempfile.TemporaryDirectory() as tmp_dirname:
          with patch(
              "transformers.models.rag.retrieval_rag.load_dataset"
          ) as mock_load_dataset:
              mock_load_dataset.return_value = self.get_dummy_dataset()
              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 10 for calling the RagRetrieverTest obj's underlying member method code with example usage: obj.test_canonical_hf_index_retriever_save_and_from_pretrained() without return types