code: def test_step(self, batch_tuple, batch_idx):
      return self._step(batch_tuple[0], batch_idx, "test")
  
imports: 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
  from .dataset import MUSTC
label_desc: Use image node_id 13 for calling the MuSTCRNNTModule obj's underlying member method code with example usage: obj.test_step(batch_tuple, batch_idx) and returns: self