How do I check if an ignition coil is bad in my 1997 Ford Taurus Sho V8?

I have a 1997 Ford Taurus Sho V8. It takes forever to start or it starts then dies over and over. Sometimes after it finally starts, it will run for a while perfect then lose power again and dies. I took it to a mechanic shop and was told that one of the ignition coil is bad but they can't tell which one so I would have to change all four. If possible I would like to know how to check them to find out which one is faulty also how much Ignition coils does this car uses? I looked inside and I could only identified 4 as seen online.