Surely they must've tested the ILS prior to an ILS landing?
And if the tests fail? Do they not land?
I'm sure there are all kinds of very unlikely scenarios. e.g. the radar antenna plate breaking off and sitting in front of the loc and G/S antennas. In this case, perhaps there would be too much shielding for the aircraft's ILS antennas to get a strong enough signal for the entire length of the glidepath and rollout?
I'm not familiar with the A320. How does the A320 handle loss of ILS signals (display pointers removed? flags?)? How does the system handle slightly or greatly disagreeing commands (between ILS systems). Whatever, I assume the crew, in most circumstances, would be able to determine if the signals are valid (i.e. by the aircraft telling them so and by manual periodic height/distance-from-threshold crosschecks).
The ILS antenna can be seen in that photo of the aircraft in the hangar on the previous page. The item which looks like a bathroom towel rail below the radar antenna is the Localizer antenna. The somewhat smaller one below that is the Glideslope antenna. Typically, these types of antennas contain two elements for two ILS systems. Does the A320 have a third ILS system?