Coil pack

How do you know when you have a bad coil pack?

i have a random cylinder misfiring. I changed the spark plugs last week and have 8mm spark plug wires that i put in about a year ago if even that. next thing to go to is my coil pack. but i dont want to replace it if its good. how do i know if it needs replacing?

had same code check vaccum lines first or take module to the zone for check buy a coil and trade out or find in you brand of service manual how to test your coils

had same code check vaccum lines first or take module to the zone for check buy a coil and trade out or find in you brand of service manual how to test your coils