marcinek, we are on the same page in regards to the usefulness (or rather lack there of) of 'spine whacking.
Maybe there is some language barrier going on. 
But, unless I'm loopy, the guy said the spine whack test is useful, because it will tell you if the lock on your blade may fail during an encounter when your opponent whacks the spine of your deployed blade.
The only way that could happen is if the bad guy makes some downward strike towards you and misses you entirely, but manages to deal a direct hit to the 1/8 inch thick, 3-4 inch long target sticking out of your hand, or if you are fending off blows with the spine of your folder. Why would the spine be pointed towards the bad guy? You "hurt" with the pointy or sharp part...not the spine.
Its an irrelevant test. Its like testing how well you can make a sunny-side up quails egg on your blade. Sure, you can test it, but so what?
Uhhh, my post was meant purely as a humorous comment. The imperative word is 'whacky' (and the smily icon).
I mistankenly believed you to have a sense of humour. Sorry about that.
As you believe that there is a language barrier, there is an explanation for the word for you below:
Merriam-Webster: Whacky also wacky
wacky adjective \ˈwa-kē\
: amusing and very strange
Definition of WACKY
absurdly or amusingly eccentric or irrational : crazy <wacky ideas> <a wacky comedian>
— wack·i·ly adverb
— wack·i·ness noun
See wacky defined for English-language learners »
Variants of WACKY
wacky also whacky
Examples of WACKY
My wacky aunt takes a swim before the lake freezes every winter.
the wacky world of his imagination
Origin of WACKY
perhaps from English dialect whacky fool
First Known Use: circa 1935
Related to WACKY
Synonymsbizarre, bizarro, cranky, crazy, curious, eccentric, erratic, far-out, funky, funny, kinky, kooky (also kookie), offbeat, off-kilter, off-the-wall, outlandish, out-of-the-way, outré, peculiar, quaint, queer, queerish, quirky, remarkable, rum [chiefly British], screwy, spaced-out, strange, odd (also whacky), way-out, weird, weirdo, wild
http://www.merriam-webster.com/dictionary/whacky?show=1&t=1386187242