code: def test_StackLSTM(self):
      lstm_dim = 100
      lstm_num_layers = 2
  
      element_root = Element("Root")
      element_node = Element("Node")
  
      lstm = nn.LSTM(lstm_dim, lstm_dim, num_layers=lstm_num_layers)
      empty_embedding = torch.zeros(1, lstm_dim)
      stackLSTM = StackLSTM(lstm)
  
      stackLSTM.push(empty_embedding, element_node)
      self.assertEqual(len(stackLSTM), 1)
      self.assertEqual(stackLSTM.element_from_top(0), element_node)
      self.assertEqual(stackLSTM.element_from_top(1), element_root)
      self.assertEqual(
          stackLSTM.embedding().shape, empty_embedding.shape
      )
  
      self.assertEqual(stackLSTM.pop()[1], element_node)
      self.assertEqual(len(stackLSTM), 0)
      self.assertEqual(stackLSTM.element_from_top(0), element_root)
      self.assertTrue(
          torch.equal(stackLSTM.embedding(), empty_embedding)
      )
  
imports: import unittest
  from collections import Counter
  import torch
  import torch.nn
  from pytext.common.constants import Stage
  from pytext.config.module_config import PoolingType
  from pytext.legacy.vocab import Vocab
  from pytext.models.embeddings import DictEmbedding, EmbeddingList, WordEmbedding
  from pytext.models.semantic_parsers.rnng.rnng_data_structures import CompositionalNN, CompositionalSummationNN, Element, ParserState, StackLSTM
  from pytext.models.semantic_parsers.rnng.rnng_parser import RNNGParser
label_desc: Use image node_id 1 for calling the RNNGDataStructuresTest obj's underlying member method code with example usage: obj.test_StackLSTM() without return types