code: def test_cython_with_timestamp_and_nat(op, data):
      # https://github.com/pandas-dev/pandas/issues/19526
      df = DataFrame({"a": [0, 1], "b": [data, NaT]})
      index = Index([0, 1], name="a")
  
      # We will group by a and test the cython aggregations
      expected = DataFrame({"b": [data, NaT]}, index=index)
  
      result = df.groupby("a").aggregate(op)
      tm.assert_frame_equal(expected, result)
  
imports: import numpy
  import pytest
  from pandas.core.dtypes.common import is_float_dtype, is_integer_dtype
  import pandas
  from pandas import DataFrame, Index, NaT, Series, Timedelta, Timestamp, bdate_range
  import pandas._testing
  import pandas.core.common
label_desc: Use image node_id 11 for calling a global function with example usage: test_cython_with_timestamp_and_nat(op, data) without return types