She had tested it of course. When she visited 12 Grimmauld Place, she had brought it with her. One evening, with her heart in her throat,  she had asked Ginny to go get something out of her trunk to see if the enchantment worked. When Ginny had returned to the room with the scarf in hand, Hermione decided to trust it with her now extensive Dark Arts book collection, as well as with the Dark objects she had begun to both collect and make. 