def METHOD_NAME(self):
    """Compare to Willmer 2018."""
    bp = (bandpass('johnson v'), bandpass('cousins i'))
    vega = Vega.from_default()
    lambda_eff, ci = vega.color_index(bp, u.ABmag)
    # I bandpass seems to be very different:
    assert np.allclose(lambda_eff.to('AA').value,
                       [5476, 7993], atol=150)
    assert np.isclose(ci.value, -0.427, atol=0.02)