Crash test bass playing is not that complicated, for most of the stuff (except where the bass line is signature, like in Another One Bites The Dust, or is essential to the song, like in Alive by Pearl Jam). Here is how I do it:
The main thing is this: if it is rock music, there is 75% chances the root note at a given moment is either G, C or D, 20% extra chances for A or E.
By experience you can build an ear for finding the correct root note pretty quickly.
After that, one good practice technique is to hum a bass line, or little bits, and then to try to reproduce it. Sometimes you think of the coolest bass lines, and doing that breaks habits and plateaus, by the way.
Once you have built that talent, it's pretty easy to figure out what's been played and to reproduce it. Hum it, either out loud or in your head, and play it.
Rock and pop music is repetitive by nature, so once you get the idea, you can play most of it and improv' cool fills when you can can't figure it out. I do that for all the GnR stuff, because on top of that McDuff never plays it twice the same.
Don't forget: Rock is silly Jazz.