A plane is also capable of landing. When auto land is engaged, there is more than just one auto pilot flying the aircraft. During the process, where the A/P is engaged and approach is armed, the aircraft will intercept the localizer and glideslope (ILS landing). The system is designed in a way that it will cross check for any discrepancies. If there are any, the landing sequence will be downgraded to a CATII or NO Autoland.
Afaik, SQ's aircraft have to have an auto land every 28 days. It is not uncommon to see them done about once a week and it is recorded in the aircraft log and tracked. This is to make sure that they system is fully operational in the event of a CATIIIC landing.