Really? Which techniques? All of them? You think every technique taught in every martial art is fully proven and equally valid? I don't.
I would say that
most techniques taught in a martial arts school
could work, given the right context and circumstances. That doesn't mean that they are all good and any failure to apply them is down to the individual being able to hold up under pressure.
I wrote a blog post a while back about
high-percentage vs low-percentage techniques.
Some techniques are relatively useful and reliable in a wide variety of situations and don't rely on having skill and attributes vastly superior to your opponent. Those would be high-percentage techniques.
Other techniques are useful in fewer circumstances or rely on having superior attributes. Those are lower percentage.
Some techniques can work, but are risky. Others are safer and carry less of a penalty for failure.
Some techniques can be effective, but only in certain specific circumstances. Depending on the instructor, those circumstances may not be correctly explained.
Some techniques were valid as applied in their original context, but through generations of teachers who have never used them in a combative setting, the details and understanding to make them functional have been lost.
Some techniques could theoretically work, but would require superior skill and attributes, an incompetent opponent attacking in an unnatural way, and quite a bit of luck.
When I was in the Bujinkan, I was taught some techniques that I can guarantee have never been used by anyone in a real fight ever and never will be. That can happen when an instructor gets creative working with a compliant uke who feeds a highly stylized and unrealistic attack. (I'm not dissing everything taught in the Bujinkan, just some specific moves.)
Testing a technique is about establishing where it falls in the categories above. You really need a community of martial artists testing the techniques in a variety of settings over time to do it right. If I find a technique that works well for me, but only 1% of practitioners can get it to work, then it's probably not the best move to make the mainstay of my schools curriculum. Contrariwise, there might be another technique that just isn't reliable for me, but works well for lots of other people.