code: def test_constructor_empty(self):
      idx = PeriodIndex([], freq="M")
      assert isinstance(idx, PeriodIndex)
      assert len(idx) == 0
      assert idx.freq == "ME"
  
      with pytest.raises(ValueError, match="freq not specified"):
          PeriodIndex([])
  
imports: import numpy
  import pytest
  from pandas._libs.tslibs.period import IncompatibleFrequency
  from pandas.core.dtypes.dtypes import PeriodDtype
  from pandas import Index, NaT, Period, PeriodIndex, Series, date_range, offsets, period_range
  import pandas._testing
  from pandas.core.arrays import PeriodArray
label_desc: Use image node_id 17 for calling the TestPeriodIndex obj's underlying member method code with example usage: obj.test_constructor_empty() without return types