def METHOD_NAME(df_separate_lat_long_columns: pd.DataFrame) -> None:
    df_clean = clean_lat_long(
        df_separate_lat_long_columns, lat_col="messy_lat", long_col="messy_long", split=True
    )
    df_check = df_separate_lat_long_columns.copy()
    df_check["messy_lat_clean"] = [np.nan, 41.5, -41.0, 80.0, np.nan, np.nan]
    df_check["messy_long_clean"] = [30.0, np.nan, -41.0, 80.0, np.nan, np.nan]
    assert df_check.equals(df_clean)