code: def long_dataframe():
      N, T = 2, 10
      df = pd.DataFrame(index=np.arange(N * T))
      df["time"] = (
          2
          * pd.date_range(
              "2021-01-01 00:00", freq="1H", periods=T
          ).to_list()
      )
      df["target"] = np.random.normal(size=(N * T,))
      df["item"] = T * ["A"] + T * ["B"]
      df["stat_cat_1"] = T * [0] + T * [1]
      df["dyn_real_1"] = np.random.normal(size=(N * T,))
      return df
  
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 3 for calling a global function with example usage: long_dataframe() and returns: df