code: def test_na_substitution(self):
      pass
  
imports: from io import BytesIO, StringIO
  import numpy
  import pytest
  import pandas._libs.parsers
  from pandas._libs.parsers import TextReader
  from pandas.errors import ParserWarning
  from pandas import DataFrame
  import pandas._testing
  from pandas.io.parsers import TextFileReader, read_csv
  from pandas.io.parsers.c_parser_wrapper import ensure_dtype_objs
label_desc: Use image node_id 17 for calling the TestTextReader obj's underlying member method code with example usage: obj.test_na_substitution() without return types