def METHOD_NAME(self):
    values = [
        (("-12 nm", "m"), ("-12", "n", "m")),
        (("-12 nm", "s"), ("-12 nm", None, None)),
        (("12 u", "s"), ("12", u"µ", None)),
        (("12 m", "s"), ("12", "m", None)),
        (("0.12 rad", "s"), ("0.12 rad", None, None)),
        (("0.12 rad", "rad"), ("0.12", None, "rad")),
    ]
    for args_in, exp_out in values:
        self.assertEqual(units.decompose_si_prefix(*args_in), exp_out)