code: def df_int_idx():
      """Create timeseries with integer index, unequally spaced."""
      return pd.DataFrame(
          data={"y": [1, 1, 1, 1, 1]}, index=[1, 2, 3, 5, 9]
      )
  
imports: import pandas
  import pytest
  from pandas.testing import assert_frame_equal
  from sktime.transformations.series.time_since import TimeSince
  from sktime.utils._testing.hierarchical import _make_hierarchical
label_desc: Use image node_id 1 for calling a global function with example usage: df_int_idx() and returns: pd