def METHOD_NAME():
    # `difference` comparison
    post_df = pp.compare(
        df=timeseries_df2,
        source_columns=["y"],
        compare_columns=["z"],
        compare_type=PPC.DIFF,
    )
    """
               label    y     z  difference__y__z
    2019-01-01     x  2.0   2.0               0.0
    2019-01-02     y  2.0   4.0              -2.0
    2019-01-05     z  2.0  10.0              -8.0
    2019-01-07     q  2.0   8.0              -6.0
    """
    assert post_df.equals(
        pd.DataFrame(
            index=timeseries_df2.index,
            data={
                "label": ["x", "y", "z", "q"],
                "y": [2.0, 2.0, 2.0, 2.0],
                "z": [2.0, 4.0, 10.0, 8.0],
                "difference__y__z": [0.0, -2.0, -8.0, -6.0],
            },
        )
    )
    # drop original columns
    post_df = pp.compare(
        df=timeseries_df2,
        source_columns=["y"],
        compare_columns=["z"],
        compare_type=PPC.DIFF,
        drop_original_columns=True,
    )
    assert post_df.equals(
        pd.DataFrame(
            index=timeseries_df2.index,
            data={
                "label": ["x", "y", "z", "q"],
                "difference__y__z": [0.0, -2.0, -8.0, -6.0],
            },
        )
    )