This picture, shot outdoors for convenience, simply shows what the setup using blocks of wood, ruler, and a home-made target to focus on looks like. I normally test AF accuracy indoors under conditions of low illumination (approximately EV3 to EV4). The small block on top is at 45 degrees relative to the long 4x4 piece of wood. Please note the optical axis of the lens must be "absolutely" perpendicular to the small block of wood the AF target is taped to.

I highly recommend you test your lenses at a magnification of X10 (specifically -1/10), or there abouts; it is my understanding that this is the magnification Canon uses to test/calibrate lens AF performance (but I always reserve the right to be wrong).

Note, any magnification of your choice if okay but I'd recommend you maintain a constant "known" value so that you can always go back and repeat the test if you sense any degradation in the AF performance of either your lens or camera body.

Given the focal length of the lens and magnification chosen for the AF test, you can calculate the total distance (T) from the sensor plane to the object from the following equation.

T = (F/R)*(R+1)^2

Where "R" is the absolute value of the inverse of the magnification and "F" is the focal length of the lens.

For example, if the object distance is 10 times the image distance, the magnification is -(1/10); so the value for "R" becomes 10 and the total distance is given by (F/10)*(11)^2 which is F*(12.1).