Yes, you can't see the starter motor by looking down inside the engine bay, nor by a quick look underneath.
From above, all the intake components block your view, and underneath a drive shaft and other things obscure it..
I think it's a 4+ hr. job to R&R, so you want to eliminate simpler possibilities first.
Of reports on this forum that had similar symptoms, the end result has been a few surprising things, such as:
- an engine control sensor gone bad and locked out the start protocol
- transponder in the key failed
- battery tested good still unable to energize the starter (more likely if continuous clicks)
It's worth checking Fuse #14 to see if that has blown as it controls the immobilizer and/or the EWS.
Failed X3 starter motors are not unheard of but not too common.
If the warm weather had anything to do with it, maybe the battery electrolyte evaporated a bit.
Battery testing is not a very exact science. I'd charge it up fully and try again before anything else.