def METHOD_NAME(dataframe):
    """Test currency inflation updates existing column."""
    initialval = dataframe["a"].sum()
    # Pulled raw values from API website for USA 2018 and 2015
    inflator = _inflate_currency("USA", currency_year=2018, to_year=2015)
    df = dataframe.inflate_currency(
        "a",
        country="USA",
        currency_year=2018,
        to_year=2015,
        make_new_column=False,
    )
    updatedval = df["a"].sum()
    assert (initialval * inflator) == pytest.approx(updatedval)