def METHOD_NAME():
    reg_sky = CircleSkyRegion(SkyCoord(1, 2, unit='deg'), 5 * u.deg)
    reg = Regions([reg_sky])
    match = 'Sky regions cannot be serialized'
    with pytest.warns(AstropyUserWarning, match=match):
        result = reg.serialize(format='fits')
        assert len(result) == 0
    reg_pix = CirclePixelRegion(PixCoord(10, 10), 5)
    reg = Regions([reg_sky, reg_pix])
    match = 'Sky regions cannot be serialized'
    with pytest.warns(AstropyUserWarning, match=match):
        result = reg.serialize(format='fits')
        assert len(result) == 1