def METHOD_NAME():
    """
    This test performs a raw (no EllipseFitter), 1-step correction in
    one single ellipse coefficient.
    """
    # pick first guess ellipse that is off in just
    # one of the parameters (eps).
    sample = EllipseSample(DATA, 40.0, eps=2 * 0.2)
    sample.update(DEFAULT_FIX)
    s = sample.extract()
    harmonics = fit_first_and_second_harmonics(s[0], s[2])
    _, a1, b1, a2, b2 = harmonics[0]
    # when eps is off, b2 is the largest (in absolute value).
    assert abs(b2) > abs(a1)
    assert abs(b2) > abs(b1)
    assert abs(b2) > abs(a2)
    correction = (b2 * 2.0 * (1.0 - sample.geometry.eps)
                  / sample.geometry.sma / sample.gradient)
    new_eps = sample.geometry.eps - correction
    # got closer to test data (eps=0.2)
    assert_allclose(new_eps, 0.21, atol=0.01)