> Do I understand this? A purely reductionist view of my understanding: this is quantified as "the amount of will to live"? If my understanding is proper, how do you measure this without killing people? I grok that it is an extreme example, I am attempting to glean applicability of such an experiment to humans.

I mean in this is one model and typically a "result" means several models are all consistent with the researcher's mental model of the thing. But yes, the forced swim test is one measure of "will to live" and it's treated as that because of similarities to "that which we call 'depression'" or whatever

It is better than nothing, unless one takes it too seriously.

[0] mice float, they don't drown when they give up, assuming you take them out quickly enough [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4401172/ [2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3353513/