code: def state_structure(self):
      return C.STEP_STATE + C.STEP_STATE
  
imports: from typing import List, Optional
  from typing import Tuple
  import numpy
  import pytest
  import torch
  import numpy
  import sockeye.beam_search
  import sockeye.constants
  import sockeye.lexicon
  import sockeye.utils
label_desc: Use image node_id 2 for calling the _TestInference obj's underlying member method code with example usage: obj.state_structure() and returns: unknown