The most sensitive test of lens quality is when you image point sources.
Stars are best, but you need a tracking equatorial mount for best results, as stars are dim and the Earth turns noticeably in exposures over a few seconds.
I often substitute distant urban lights for stars. Tilt your tripod-mounted camera so that the urban skyline runs diagonally from corner to corner of the frame. Then shoot at different apertures. Maybe 1 sec at f2.8, 2 sec at f4, ...etc. Use everything you can to reduce vibration - mirror lockup, remote release, self timer...
When you examine the images you may be shocked by how bad the point-lights are in the corners, expecially wide open; but also encouraged at how much better they get 1 or 2 stops closed down. As I said, this is a very sensitive test.
What I also like about this is that it is charge-free and fuss-free - no printing out and mounting of test charts at special distances and positions, or any of that chicanery. Just pick your spot, arrive in the evening and shoot. Society's addiction to wasteful light pollution has given you a gigantic, free "test chart".
Here's an example from my film days - same lens, first f2.8 (bad coma and oblique spherical aberrations) then f4 (very well cleaned up).