code: def test_infer_freq_from_first_element(self):
      msg = "Period with BDay freq is deprecated"
      with tm.assert_produces_warning(FutureWarning, match=msg):
          start = Period("02-Apr-2005", "B")
          end_intv = Period("2005-05-01", "B")
          period_range(start=start, end=end_intv)
  
          # infer freq from first element
          i2 = PeriodIndex([end_intv, Period("2005-05-05", "B")])
      assert len(i2) == 2
      assert i2[0] == end_intv
  
      with tm.assert_produces_warning(FutureWarning, match=msg):
          i2 = PeriodIndex(
              np.array([end_intv, Period("2005-05-05", "B")])
          )
      assert len(i2) == 2
      assert i2[0] == end_intv
  
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 28 for calling the TestPeriodIndex obj's underlying member method code with example usage: obj.test_infer_freq_from_first_element() without return types