code: def test_optional_args():
      kwargs = {
          "process": [
              {
                  "type": "channel_selector",
                  "train_channel": 0,
                  "eval_channel": 1,
                  "axis": 0,
              }
          ],
          "mode": "sequential",
      }
      preprocessing = Transformation(kwargs)
      assert preprocessing(np.array([100, 200]), train=True) == 100
      assert preprocessing(np.array([100, 200]), train=False) == 200
  
file_path: espnet/test/test_transform.py
imports: import kaldiio
  import numpy
  import pytest
  from espnet.transform.add_deltas import add_deltas
  from espnet.transform.cmvn import CMVN
  from espnet.transform.functional import FuncTrans
  from espnet.transform.spectrogram import logmelspectrogram
  from espnet.transform.transformation import Transformation
label_desc: Use image node_id 2 for calling a global function with example usage: test_optional_args() without return types