Strand Dead

UPDATE: My Mom sent me the following.  Any tried one before?

http://www.lightkeeper.biz/

Ah, it's that time of year... men cursing to themselves, fighting with globs of xmas lights, and nearly falling off ladders. Today I spent nearly 4 hours going through every bulb on a pre-lit Christmas tree trying to find why one section wasn't lit. I pulled out every bulb and swap it with a good bulb, and worked my way down the tree. My fingers are sore. I have blisters. And I still never found the problem. The solution? I drove over to Big Lots, bought 2 new strands, and ran them in the bare spots.

The question is, how do you diagnose a problem like this? I'm sure I made it worse by removing each bulb and putting it back in. What's the chances only 1 bulb was the culprit by the time I got done? There's got to be a better way? Thoughts?  I set my non-pre-lit tree up in less than an hour.  I'm thinking having the lights separate is a good thing.  Kinda like buying one of those TVs with the DVD player built in.  You're just asking for trouble.