How can I tell if I have properly patched a tube? (specifically a 2" mt. bike tube) I normally swap out a the tube on the trail if I get a flat and then patch at home. So that leaves me with a patched tube ready to put in a tire and I'd like to test it without having to swap out a tube ('cause I'm lazy :).

I thought that perhaps I could just inflate it but I'm concerned that without the opposing pressure of the tire it might blow an otherwise solid patch.
I do like you do when riding, and I usually save up my tubes with holes and patch a bunch of them all at once. That way I can use a tub of water to both find the holes, and can go back through them after patching and test to see if they are holding air.

If I have any doubt after patching a tube, I give it a little time to cure and then I pump it up and hang it from a hook in my garage overnight to see if it loses air.