The name "Testificate" was originally seen as the name hovering above the villager NPCs during their initial release in Beta 1.9 Pre-release 1. The name hovered above there heads in a similar fashion to player names in multiplayer.
While the name was removed in Beta 1.9 Pre-release 2, the name stuck as a fan name thanks in part to Yogscast and the community as a whole.
I built my own house next to a NPCvillage and had an infestation of testificates in my building.
Often associated with a severe case of swalls/mustynut, a condition in which ones scrote will stick to the sides of the thighs. This normally causes the victim to do a quick "lift and shift" or a silly leg twitch, on the sly, while walking.
It was so hotoutside yesterday that my swalls developed into an unbeatable case of testickies.