It's not exactly done with a NTHSA-approved methodology - don't try this at home, kids! - but this real-world torture test of a Nissan LEAF battery cell shows just how much abuse these things can take without much dangerous happening. Quite impressive, though I wouldn't go as far as to compare it with the few Tesla Model S fires (which I put in context here) because the situation is quite different, with only one cell getting relatively low-energy impacts over a small area compared to a whole battery pack getting a high-energy impact from a large piece of metal debris or a brick wall or whatever, and on top of that, in one of the fires the firefights drilled holes in the battery, which made things more spectacular than they otherwise would have been.
But even without comparing it to anything else, it stands on its own as pretty impressive. Kudos Nissan!
That's a current technology battery. Future ones might be almost completely non-flammable if some recent lab breakthroughs can be commercialized. For more details, see: Safer non-flammable lithium-ion batteries are coming.