code: def test_to_csv_from_csv3(self):
      with tm.ensure_clean("__tmp_to_csv_from_csv3__") as path:
          df1 = DataFrame(
              np.random.default_rng(2).standard_normal((3, 1))
          )
          df2 = DataFrame(
              np.random.default_rng(2).standard_normal((3, 1))
          )
  
          df1.to_csv(path)
          df2.to_csv(path, mode="a", header=False)
          xp = pd.concat([df1, df2])
          rs = read_csv(path, index_col=0)
          rs.columns = [int(label) for label in rs.columns]
          xp.columns = [int(label) for label in xp.columns]
          tm.assert_frame_equal(xp, rs)
  
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 4 for calling the TestDataFrameToCSV obj's underlying member method code with example usage: obj.test_to_csv_from_csv3() without return types