snapper mower:interlock module - how test?

Snapper 1438H Hydro, rear-engine riding mower.
Thing yesterday just quit. Engine turns over, but no spark to the sparkplug. The three safety switches (seat,PTO,and pedal) check out OK. Next item up the line is the INTERLOCK MODULE...
All the safety switches tie into the IM. How do I test the IM?
About the size of a chunky book of matches. Tab of a circuit board poking out plastic sealing filler. This thing have a chip in it? Ya gotta be kidding me -- an IC for the damn safety switch system? Gimme a break. $30 to replace. Up yours, Snapper.
Fed up with this mower. "Legendary Snapper"... yeah, right. Something going wrong with it about every other time we use it, if not every time...
System fuse is ok. Will check the key switch next. There's also the ignition coil... how do I check the ignition coil?
Dagnabbit -- all on the frigging holiday weekend too.
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