Randy's test is good!
Here's another one.
Put the cue ball on the spot. Point the cue through the center of the cue ball directly at the center diamond on the end rail. Have one of your friends line you up to make sure you are lining up straight at the center spot through the middle of the cue ball.
Now, move the whole cue to the right or the left by about 2 tips of english. You should now be 2 tips off center on the cue ball and lined up 2 tips off the center diamond on the end rail. Have your friend check again.
Now, hit the ball with a soft to medium break speed. You want to hit it hard enough that the spin won't make the cue ball curve. Mark where the cue ball hits the end rail. Your buddy who lined you up can do this for you.
That's how much squirt your cue shaft has. You will find some out several inches and some down near or under 1 inch depending on how hard you hit it. If you find that you aren't hitting out that far, you are most likely twisting during the stroke to compensate for the squirt. Have your buddy watch to make sure you go straight through the cue ball and point towards that 2 tip aiming point.
I have done this with hundreds of people over the years and over 95% of them are amazed by it.