ya, you can have a spark thats too weak to actually fire the engine. a white/blue spark is nice and strong, a yellow spark is on the weak side. or there's a super cheap spark tester that has an adjustable gap and you put it on the wire, set the gap and you can see the spark jump, if it jumps at a smaller gap but not in spec, then the spark could be too weak.
it comes with a little spec sheet usually for different vehicles. the gap on the tool is usually anywhere from zero to a little over an inch, its not like trying to look at a spark plug.