code: def test_numpy_string_dtype(self):
      data = """\
  a,1
  aa,2
  aaa,3
  aaaa,4
  aaaaa,5"""
  
      def _make_reader(**kwds):
          if "dtype" in kwds:
              kwds["dtype"] = ensure_dtype_objs(kwds["dtype"])
          return TextReader(
              StringIO(data), delimiter=",", header=None, **kwds
          )
  
      reader = _make_reader(dtype="S5,i4")
      result = reader.read()
  
      assert result[0].dtype == "S5"
  
      ex_values = np.array(
          ["a", "aa", "aaa", "aaaa", "aaaaa"], dtype="S5"
      )
      assert (result[0] == ex_values).all()
      assert result[1].dtype == "i4"
  
      reader = _make_reader(dtype="S4")
      result = reader.read()
      assert result[0].dtype == "S4"
      ex_values = np.array(
          ["a", "aa", "aaa", "aaaa", "aaaa"], dtype="S4"
      )
      assert (result[0] == ex_values).all()
      assert result[1].dtype == "S4"
  
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 18 for calling the TestTextReader obj's underlying member method code with example usage: obj.test_numpy_string_dtype() and returns: TextReader