1998 Toyota Camry COIL THAT SITS ON TOP OF SPARKPLUGS 2,4 A

I have been experiencing a rough idle. Some times it's not as rough as other times. I was told that all the cylinders were not firing properly and that I probably need a tune up. I have replaced the spark plugs and wires. I have replaced the air filter and checked for vaccum leaks. I am comtiplating on changing the coils but they are so exspensive. Is there a way that I can test the coils that I have on the car now?

Thanks
J