code: def get_dummy_legacy_index_retriever(self):
      dataset = Dataset.from_dict(
          {
              "id": ["0", "1"],
              "text": ["foo", "bar"],
              "title": ["Foo", "Bar"],
              "embeddings": [
                  np.ones(self.retrieval_vector_size + 1),
                  2 * np.ones(self.retrieval_vector_size + 1),
              ],
          }
      )
      dataset.add_faiss_index(
          "embeddings",
          string_factory="Flat",
          metric_type=faiss.METRIC_INNER_PRODUCT,
      )
  
      index_file_name = os.path.join(
          self.tmpdirname,
          "hf_bert_base.hnswSQ8_correct_phi_128.c_index",
      )
      dataset.save_faiss_index(
          "embeddings", index_file_name + ".index.dpr"
      )
      pickle.dump(
          dataset["id"], open(index_file_name + ".index_meta.dpr", "wb")
      )
  
      passages_file_name = os.path.join(
          self.tmpdirname, "psgs_w100.tsv.pkl"
      )
      passages = {
          sample["id"]: [sample["text"], sample["title"]]
          for sample in dataset
      }
      pickle.dump(passages, open(passages_file_name, "wb"))
  
      config = RagConfig(
          retrieval_vector_size=self.retrieval_vector_size,
          question_encoder=DPRConfig().to_dict(),
          generator=BartConfig().to_dict(),
          index_name="legacy",
          index_path=self.tmpdirname,
      )
      retriever = RagRetriever(
          config,
          question_encoder_tokenizer=self.get_dpr_tokenizer(),
          generator_tokenizer=self.get_bart_tokenizer(),
      )
      return retriever
  
imports: import json
  import os
  import pickle
  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 9 for calling the RagRetrieverTest obj's underlying member method code with example usage: obj.get_dummy_legacy_index_retriever() and returns: retriever