'In an empty L{base.PositionError} with no invariant testing, all
dilutions of positions are L{None}.'

def test_allUnset(self):

    positionError = base.PositionError()
    self.assertIsNone(positionError.pdop)
    self.assertIsNone(positionError.hdop)
    self.assertIsNone(positionError.vdop)
