code: def get_dpr_ctx_encoder_tokenizer(self) -> DPRContextEncoderTokenizer:
      return DPRContextEncoderTokenizer.from_pretrained(
          os.path.join(self.tmpdirname, "dpr_tokenizer")
      )
  
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 3 for calling the RagRetrieverTest obj's underlying member method code with example usage: obj.get_dpr_ctx_encoder_tokenizer() and returns: DPRContextEncoderTokenizer