code: def test_ngroup_empty(self):
      ge = DataFrame().groupby(level=0)
      se = Series(dtype=object).groupby(level=0)
  
      # edge case, as this is usually considered float
      e = Series(dtype="int64")
  
      tm.assert_series_equal(e, ge.ngroup())
      tm.assert_series_equal(e, se.ngroup())
  
imports: from itertools import product
  from string import ascii_lowercase
  import numpy
  import pytest
  from pandas import DataFrame, Index, MultiIndex, Period, Series, Timedelta, Timestamp, date_range
  import pandas._testing
label_desc: Use image node_id 9 for calling the TestCounting obj's underlying member method code with example usage: obj.test_ngroup_empty() without return types