code: def test_to_csv_path_is_none(self, float_frame):
      # GH 8215
      # Make sure we return string for consistency with
      # Series.to_csv()
      csv_str = float_frame.to_csv(path_or_buf=None)
      assert isinstance(csv_str, str)
      recons = read_csv(StringIO(csv_str), index_col=0)
      tm.assert_frame_equal(float_frame, recons)
  
imports: import csv
  from io import StringIO
  import os
  import numpy
  import pytest
  from pandas.errors import ParserError
  import pandas
  from pandas import DataFrame, Index, MultiIndex, NaT, Series, Timestamp, date_range, period_range, read_csv, to_datetime
  import pandas._testing
  import pandas.core.common
  from pandas.io.common import get_handle
label_desc: Use image node_id 43 for calling the TestDataFrameToCSV obj's underlying member method code with example usage: obj.test_to_csv_path_is_none(float_frame) without return types