I believe they can boot up from an external device, or over network, and run the tests. There's absolutely no reason to give them your password. I went through

I believe they can boot up from an external device, or over network, and run the tests. There's absolutely no reason to give them your password. I went through a battery replacement (out of warranty, but still covered by Apple), and I was never asked for the password. But maybe they didn't even bother to run tests, since it was literally pushing the keyboard up ever so slightly, the touch pad wouldn't click anymore (haptic feedback very weak) and the bottom plate was bulging out. It was pretty obvious what is up. The nice thing tho, I ended up with a new battery, new keyboard, new touchpad and new bottom plate. I guess every (most?) cloud has a silver lining? :)