How to tell if front axel U-joints are bad?

I've found writeups on changing front U joints in a D30, but not on how to tell if they're bad.

2000 XJ sport. In doing my pre-trip check up on the XJ, I took a look at the U joints in the front axel (D30). I remember having at least one side replaced by a shop a couple of years ago. I don't put a ton of miles on the jeep - I only have about a 20 mile RT drive to work.

What I did was the following: with the Jeep in park, and tires on the ground, I grasped the axel shaft with my hand and pulled/twisted it. I could make both sides move, and clunk a bit. Should there be any play at all? I haven't noticed any clunking when I drive. I know it's better to change them at home rather than on the trail, but I have a lot to do before my trip, and if they can wait, that would be great. I've never done them before.

shouldn't be any play. change 'em before you use them (would probably last a while in 2wd, but they'll probably break in 4wd)

Should be no play, often you will feel it through the steering wheel when makeing shallow turns when they go bad.
Doesn't matter if you replaced them last year, if they are never greased they don't last long, they are always working.

Xwhatever, replace them before you do anything with them. If they blow up on the trail you're more than likely going to end up replacing the inner shaft and stub shaft as well because the ears will collide and/or get egged out. If you REALLY lay on the skinny pedal, you can get bonus points and end up replacing the balljoints as well.

You've got a late model (95 and later have the right shafts for this iirc), so you can put Spicer 760x joints in without upgrading your shafts. Use greasable joints and keep them greased, they will last longer than "lifetime greased" joints.