code: def _test_collate_fn(self, samples: List):
      return self._valid_collate_fn(samples), [
          sample[2] for sample in samples
      ]
  
imports: import os
  from functools import partial
  from typing import List
  import sentencepiece
  import torch
  import torchaudio
  from common import Batch, batch_by_token_count, FunctionalModule, GlobalStatsNormalization, piecewise_linear_log, post_process_hypos, spectrogram_transform, WarmupLR
  from pytorch_lightning import LightningModule
  from torchaudio.models import emformer_rnnt_base, RNNTBeamSearch
label_desc: Use image node_id 7 for calling the LibriSpeechRNNTModule obj's underlying member method code with example usage: obj._test_collate_fn(samples) and returns: self,  unknown