Since my prints from my Nikon and Canon cameras are 5-10 feet in length, I test all of my lenses.
I just tested a Sigma 35mm 1.4 which has been widely touted on the internet. The entire right side was out of focus. Had to return it. Fortunately, I have a Zeiss 35mm f2 that can take its place.
With mass produced lenses, and especially wide angle lenses, there can be lots of variation from copy to copy. If you want to do large prints, I recommend this test.
Print out five Word documents that have lines of type that range from 8 point up to 72 point. Be sure to indicate the size of the typeface at the end of each line.
Set your camera up on a sturdy tripod and use a heavy weight (I use one of my backpacks full of photo gear) to weigh it down. Use a shutter release cable so that you don't touch the camera when tripping the shutter. Use the magnification in live view and a loupe to manually focus the lens. Use Aperture Priority. Be sure to check focus with each aperture as there can be focus shift from one aperture to another.
Find a wall that is at least 10 feet across. Move your camera forward or back so that the wall fills the frame of your camera. Make sure your camera is the same height as the center of the wall. Put a double bubble on the flash mount and make sure the camera is level front to back and side to side.
Now mount one of the Word documents in the exact center of the wall and make sure it is also in the exact center of your live view. Also, make sure the back of your camera is parallel to the wall. On a post-it, write the name of the lens and make post-its with each aperture on them.
Using your live view, place the other four Word documents on the wall in the four corners of your frame.
Use the center document to focus the lens as best you can. Take a series of photos with every aperture of the lens. As you change the aperture, change the post-it so that you can easily see which aperture you shot.
Bring the photos into Lightroom.
On a piece of paper, list the apertures on the left side of the paper. Across the top write Center, Upper Right, Lower Right, Lower Left and Upper Left.
Double click on the photo to enlarge it to 100%. Find the smallest line of type that you can read. Write that number down for each position, and go through all the apertures.
This may sound complicated, but it now takes me just 20 minutes to test a lens.
In many cases, you will see the center is sharp and clear with good contrast, but the corners are distorted, blurred, smeared, or full of chromatic aberration. Since I want my prints sharp corner to corner, I return lenses with these characteristics. Even some medium and telephoto lenses may have these characteristics, but it is more common on wide angle lenses.
Once you have all your numbers written on your piece of paper, you will see that there are some optimum apertures for each lens. For most of my lenses, this is usually 5.6 to 11, but it may vary from lens to lens.
I print a small piece of paper with the name and focal length of each lens and their optimum apertures. I laminate this piece of paper with 2" wide transparent tape and stick it in my camera bag. When I am out shooting, I pick one of the optimum apertures, knowing that it will give me prints that are sharp corner to corner.
You can see my prints at http://www.photographica.us
Again, this seems laborious and complicated when written down, but it takes a short amount of time, which I find enjoyable and informative as I really get to know each lens before I take it out in the field. It also give me the opportunity to return a lens that is defective before taking lots of photos that I will never be able to print.