code: def test_csv_to_string(self):
      df = DataFrame({"col": [1, 2]})
      expected_rows = [",col", "0,1", "1,2"]
      expected = tm.convert_rows_list_to_csv_str(expected_rows)
      assert df.to_csv() == expected
  
imports: import io
  import os
  import sys
  from zipfile import ZipFile
  from _csv import Error
  import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, compat
  import pandas._testing
label_desc: Use image node_id 6 for calling the TestToCSV obj's underlying member method code with example usage: obj.test_csv_to_string() without return types