What kinds of tests can one perform on binoculars to make sure they are not defective/damaged/etc? I know about the "continuous horizontal line in both eyepieces" vertical collimation test:
http://www.birdwatching.com/optics/.../alignment.html
What else is there? Anything involving stars worth doing? Any good way to test horizontal alignment?
You will get some responses. But I think the best test is to spend a few hours in the field. If they are out of alignement, you will get eye strain. I am sensitive to looking at things too close with porros, so I avoid that test, they all look bad. But at a reasonable distance they should all be, porros and roofs, comfortable.
Tero is right, provided you have some observing experience. But newer bino users often want a simply interpretable test. I'll just speak to the stars question. I spend a lot of time looking at them myself, and I'm not the only stargazer here, but since it's not too common on this forum, their optics testing benefits may not be widely appreciated.
First, they are very sensitive indicators of collimation. Look at a bird, and if the bino is not well collimated, the eyes will go to great lengths to line the two birds up, which could fool you, until you feel the eyestrain, into thinking the bino is okay. But look at a crowded starfield, and the all the stars look pretty much alike. The eyes don't know which two points to line up, and collimation errors become quite obvious. If crowded starfields are instantly seen with aligned images, that is good news.
Second, bright point sources like stars are very severe tests of optical quality. Almost too severe, some people might say. And, stars test your eyesight along with the bino optics, and it can take some thought to figure out whether a flaw is in the bino or in yourself. But if your eyes are not astigmatic, and you use your binocular to look at a bright star, you will ideally see a compact and mostly circular blob of light. If the image is big and misshapen and blobby, or there are big spikes sticking out, that is bad. Viewing one eyed, and rotating the suspect barrel, will tell you if it's the bino at fault, or your vision.
Ron