code: def _get_new_prefix(
      self, cf, bert_spec, seq_len, do_lower_case, tokenizer
  ):
      bert_preprocessor = preprocessor.BertClassifierPreprocessor(
          seq_len=seq_len,
          do_lower_case=do_lower_case,
          uri=bert_spec.get_path(),
          model_name=bert_spec.name,
          tokenizer=tokenizer,
      )
      new_cf = bert_preprocessor._get_tfrecord_cache_files(cf)
      return new_cf.cache_prefix_filename
  
imports: import csv
  import io
  import os
  import tempfile
  from unittest import mock
  from absl.testing import parameterized
  import mock
  import numpy
  import numpy.testing
  import tensorflow
  from mediapipe.model_maker.python.core.data import cache_files
  from mediapipe.model_maker.python.text.text_classifier import bert_tokenizer
  from mediapipe.model_maker.python.text.text_classifier import dataset
  from mediapipe.model_maker.python.text.text_classifier import model_spec
  from mediapipe.model_maker.python.text.text_classifier import preprocessor
label_desc: Use image node_id 6 for calling the PreprocessorTest obj's underlying member method code with example usage: obj._get_new_prefix(cf, bert_spec, seq_len, do_lower_case, tokenizer) and returns: new_cf