code: def test_datetime_count(self):
      df = DataFrame(
          {
              "a": [1, 2, 3] * 2,
              "dates": date_range("now", periods=6, freq="min"),
          }
      )
      result = df.groupby("a").dates.count()
      expected = Series(
          [2, 2, 2], index=Index([1, 2, 3], name="a"), name="dates"
      )
      tm.assert_series_equal(result, expected)
  
imports: from datetime import datetime, timedelta
  import numpy
  import pytest
  import pytz
  import pandas
  from pandas import DataFrame, DatetimeIndex, Index, MultiIndex, Series, Timestamp, date_range, offsets
  import pandas._testing
  from pandas.core.groupby.grouper import Grouper
  from pandas.core.groupby.ops import BinGrouper
label_desc: Use image node_id 19 for calling the TestGroupBy obj's underlying member method code with example usage: obj.test_datetime_count() without return types