basically i was creating a way to get enchanted books easier and one part of it is as follows

/testfor @e[type=Item,x=-133,y=67,z=367,r=3] {OnGround:2b,Item:{id:"minecraft:writable_book"}}

i have this set to a hopper clock, but when the item is on the ground it produces this as the output

[19:12:33] item.item.writingBook did not match the required data structure

as far as i have done in the past it should work , i am in 1.8 pre though idk if that would effect it