Where to draw the line?

This question is probably the question that I consider the most. Everything we do in our daily lives is subject to this question. How much we eat or drink; how much time we spend working/playing; what time we go to bed; what we think of tax cuts/hikes proposed by the government; etc. The notion that "everything is good in moderation" is a trivial one. Where to draw the line is almost never absolute, and it always varies on a case-by-case basis.

We all agree that getting at least eight hours of sleep is a good thing. But, to say that one should never get less than eight hours of sleep, for example, would be silly. Say it's midnight and you have to wake up at eight a.m., however, there's a violent wolverine in your sock drawer. I think it's pretty obvious in this particular situation that you ought to engage in hand-to-hand combat with the wolverine until he or she is dispatched from your home. Wolverines are free to start new lives when they need to, but not with your socks. It's not prudent.

Something that I've been thinking about a lot lately is animal testing. Right off the bat, I don't like the idea of animal testing. It conjures up images of animals being given shots or giraffes wearing lipstick or whatever. It's not comforting, to say the least. But I can tweak the example to alter my intuitions drastically.

Let's say you've just been stranded on an island, and you have your neighbor's pet wolverine with you (unrelated to wolverine "A"). You just met this wolverine, and are neutral about it. You walk around with this wolverine in order to find food and water. Eventually, you come upon the only food supply on the island; bright red berries growing from an ominous looking bush. You don't know much about botany/horticulture/whatever the fuck you would call "berry science," but you're ready to believe that either (a) these berries are delicious and will sustain you, or, (b) these berries will make you sick.

You panic for a second, and then you look at your wolverine-accomplice. You realize that if you were to feed some of the berries to the wolverine and then witness the results, you could know whether or not to eat the berries. You feel guilty about it, but your overall concern is survival. "Better that the wolverine suffers than me," you think. So, what do you do? Do you test the berries on the wolverine? Or, do you abstain, because animal testing is always bad?

And, if you decide that animal testing is all right in this certain situation, when/why does it become morally just? Where do you draw the line?