code: def test_fit_transform_datetime_daily_idx_panel_output(
      df_datetime_daily_idx_panel,
  ):
      """Tests that we get the expected outputs when input is panel data."""
      transformer = TimeSince(
          start=None,
          freq="D",
          to_numeric=True,
          keep_original_columns=False,
          positive_only=False,
      )
  
      Xt = transformer.fit_transform(df_datetime_daily_idx_panel)
  
      expected = pd.DataFrame(
          data={
              "time_since_2000-01-01 00:00:00": [0, 1, 2, 0, 1, 2],
          },
          index=df_datetime_daily_idx_panel.index,
      )
      assert_frame_equal(Xt, expected)
  
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 16 for calling a global function with example usage: test_fit_transform_datetime_daily_idx_panel_output(df_datetime_daily_idx_panel) without return types