code: def test_case_1(self):
      ds = DataSet(
          [Instance(words=["hello", "world"]), Instance(words=["Jack"])]
      )
      vocab = Vocabulary().from_dataset(ds, field_name="words")
      assert len(vocab) == 5
      embed = LSTMCharEmbedding(vocab, embed_size=3)
      x = torch.LongTensor([[2, 1, 0], [4, 3, 4]])
      y = embed(x)
      assert tuple(y.size()) == (2, 3, 3)
  
imports: import pytest
  from fastNLP.envs.imports import _NEED_IMPORT_TORCH
  from fastNLP import Vocabulary, DataSet, Instance
  from fastNLP.embeddings.torch.char_embedding import LSTMCharEmbedding, CNNCharEmbedding
label_desc: Use image node_id 1 for calling the TestCharEmbed obj's underlying member method code with example usage: obj.test_case_1() without return types