How can I determine if my floppy drive is dead?

In my rebuilt PM 9600, I have been unable to successfully mount a floppy
disk since I put it all back together. Any disk I put in, within a second
or so the "Disk Is Unreadable" or whatever error appears and asks if I
want to initialise the disk, and many of these floppies mounted absolutely
fine only a few months ago when my Performa was still operational.

So, I'm leaning towards the drive being the issue. I do have 4 or 5 spare
drives so I intend to try them all out, but I've had two drives so far
behave in the same way. Is there any software test I can run to prove if
the drive is operational? Could they need a clean? Would dismantling them
and cleaning help???