code: def test_to_csv_date_format_in_categorical(self):
      # GH#40754
      ser = pd.Series(
          pd.to_datetime(["2021-03-27", pd.NaT], format="%Y-%m-%d")
      )
      ser = ser.astype("category")
      expected = tm.convert_rows_list_to_csv_str(
          ["0", "2021-03-27", '""']
      )
      assert ser.to_csv(index=False) == expected
  
      ser = pd.Series(
          pd.date_range(
              start="2021-03-27",
              freq="D",
              periods=1,
              tz="Europe/Berlin",
          ).append(pd.DatetimeIndex([pd.NaT]))
      )
      ser = ser.astype("category")
      assert ser.to_csv(index=False, date_format="%Y-%m-%d") == 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 13 for calling the TestToCSV obj's underlying member method code with example usage: obj.test_to_csv_date_format_in_categorical() without return types