code: def test_guess_datetime_format_f(input):
      # https://github.com/pandas-dev/pandas/issues/49043
      result = parsing.guess_datetime_format(input)
      expected = "%Y-%m-%dT%H:%M:%S.%f"
      assert result == expected
  
imports: from datetime import datetime
  import re
  from dateutil.parser import parse
  from dateutil.tz import tzlocal
  from hypothesis import given
  import numpy
  import pytest
  from pandas._libs.tslibs import parsing, strptime
  from pandas._libs.tslibs.parsing import parse_datetime_string_with_reso
  from pandas.compat import ISMUSL, is_platform_windows
  import pandas.util._test_decorators
  import pandas._testing
  from pandas._testing._hypothesis import DATETIME_NO_TZ
label_desc: Use image node_id 21 for calling a global function with example usage: test_guess_datetime_format_f(input) without return types