"Power testing" (试力) is an advanced concept in internal martial art as introduced in YiQuan (意拳/大成拳). It is supposed to be practiced only after one has a strong foundation in zhan zhuang, i.e. one has passed the initially power generation and storage stage with stationery forms. First question: what exactly is Power Testing?
As explained in my various zhan zhuang posts, the ultimate objective of zhan zhuang is muscles-as-one (肌肉如一). A practitioner will have the sense of power or he can feel his power (latent) at his extension muscles which are now ready to do pushing/punching works needed for any martial art. The next task is how to deliver this power in movement.
From the outside, power testing forms (which are actually rather simple forms that a seasoned practitioner can create more forms suited to his or his students' particular needs) look like simplified tai-chi forms. Like other aspects of the system of internal martial arts, the forms are not the most important aspect. Rather it is a practitioner's internal "feel" that is most important.
What then is the "internal requirement" in power testing? It is the sluggish feeling of resistance AS IF created by the requirement of moving a heavy object, associated with different bodily parts, most evidently felt being at one's hands (i.e. not limited to the hands).
It is interesting to note here that the teachings of YiQuan don't usually elaborate more on this area. A person who is really interested in this subject can perhaps turn to the teachings of tai-chi, in particular to the subject of Spinning-silk Jing (缠丝劲), in which the generation of power in motion is being activated by progressive turnings at one's ball-and-socket joints.
With a more liberal attitude towards disclosure, a modern practitioner can now turn to techniques and insights of different disciplines to devise one's practice routines. A good understanding of the gist of each discipline is therefore very important!