def METHOD_NAME():
    # test x
    normal = FITTER.approximate_normal(FITTER.x0 + R_SPHERE, FITTER.y0, FITTER.z0)
    np.testing.assert_almost_equal(normal, np.array([1, 0, 0]), decimal=3)
    # test y
    normal = FITTER.approximate_normal(FITTER.x0, FITTER.y0 + R_SPHERE, FITTER.z0)
    np.testing.assert_almost_equal(normal, np.array([0, 1, 0]), decimal=3)
    # test y+z
    normal = FITTER.approximate_normal(FITTER.x0, FITTER.y0 + R_SPHERE, FITTER.z0 + R_SPHERE)
    np.testing.assert_almost_equal(normal, np.array([0, 1, 1]) / np.sqrt(2), decimal=3)