You are referring to the section in the lens testing on page 82 titles "An Unfortunate Omission". I suppose you could test for this by checking for correct focus in the extreme corners vs. the center at the extreme ends of the contrast scale. If you have a UV filter of the proper size, try running the test both with and without the filter in place and see if there is any perceptible difference. Ask other people if they can pick out a sharper print to eliminate bias.