Ignition coil suddenly stopped sparking on any cylinder

The car had been working fine for years, then suddenly, for no apparent reason the coil suddenly stopped producing a spark, is the normal and how can I check the coil to see if it has given up the ghost. As a side not, the exhaust, which im about to change, rotted at the rear end so I have been running it without the rear silencer for the last couple of weeks so is running rich, could that be a factor. Would really appreciate soem help, im good wityh machanics, not so good with electrcs?