code: def test_token_to_char_empty_str():
      expected_m = np.array([[]], dtype=np.int32)
      m = token_to_char("")
      assert (m == expected_m).all()
  
imports: import numpy
  import pytest
  from jiant.utils.retokenize import TokenAligner, token_to_char
label_desc: Use image node_id 3 for calling a global function with example usage: test_token_to_char_empty_str() without return types