code: def tearDown(self):
      shutil.rmtree(self.tmpdirname)
  
      # clean-up as much as possible GPU memory occupied by PyTorch
      gc.collect()
      torch.cuda.empty_cache()
  
imports: import gc
  import json
  import os
  import shutil
  import tempfile
  import unittest
  from unittest.mock import patch
  import numpy
  from transformers import BartTokenizer, T5Tokenizer
  from transformers.models.bert.tokenization_bert import VOCAB_FILES_NAMES
  from transformers.models.dpr.tokenization_dpr import DPRContextEncoderTokenizer, DPRQuestionEncoderTokenizer
  from transformers.models.roberta.tokenization_roberta import VOCAB_FILES_NAMES
  from transformers.testing_utils import get_tests_dir, require_sentencepiece, require_tokenizers, require_torch, require_torch_non_multi_gpu, slow, torch_device
  from transformers.utils import cached_property, is_datasets_available, is_faiss_available, is_torch_available
  from ..bart.test_modeling_bart import BartModelTester
  from ..dpr.test_modeling_dpr import DPRModelTester
  from ..t5.test_modeling_t5 import T5ModelTester
label_desc: Use image node_id 6 for calling the RagTestMixin obj's underlying member method code with example usage: obj.tearDown() without return types