code: def test_infer_period(my_dataframe):
      ds = pandas.PandasDataset(
          my_dataframe, target="target", freq="1D"
      )
      for entry in ds:
          assert entry["start"] == pd.Period("2021-01-01", freq="1D")
  
imports: import io
  from typing import Callable, List, Union
  import pandas
  import numpy
  import pytest
  from gluonts.dataset import pandas
  from gluonts.testutil.equality import assert_recursively_equal
label_desc: Use image node_id 10 for calling a global function with example usage: test_infer_period(my_dataframe) without return types