def METHOD_NAME():
    da = array1d_linspace()
    dim = da.dim
    da = sc.concat([da, da + da], 'extra_dim')
    mask = sc.array(dims=['extra_dim'], values=[False, True])
    da.masks['mask'] = mask.copy()
    sos = butter(da.coords[dim], N=4, Wn=4 / da.coords[dim].unit)
    out = sosfiltfilt(da, dim, sos=sos)
    assert sc.identical(out.masks['mask'], mask)