'L{SerialNumber.__add__} returns a wrapped value when s1 plus the s2
would result in a value greater than the C{maxVal}.'

def test_maxVal(self):

    s = SerialNumber(1)
    maxVal = ((s._halfRing + s._halfRing) - 1)
    maxValPlus1 = (maxVal + 1)
    self.assertTrue((SerialNumber(maxValPlus1) > SerialNumber(maxVal)))
    self.assertEqual(SerialNumber(maxValPlus1), SerialNumber(0))
