The tag {Inventory:[{Count:1b,Slot:1b,Damage:0s,id:writable_book}]} doesn't exit

Be sure that:
a) Your book is indeed in item slot 2! 2 not 1, since in programming the first thing has a number 0. _
b) Your book has a damage value of 1.
Also I don't remember, but try using book's ID instead of name.

This is probably related to MC-30976.

Probably you have to specify the complete content of the Inventory tag and you'll have to provide the datatypes ("Slot:1b")

I put the command /testfor @p {Inventory:[{Count:1,Slot:0b,Damage:0,id:writable_book}]}
and still doesnt work.

The output:
[15:07:56] roydbt did not match the required data structure

here is fix version and make should do in right order and right data tags too.

/testfor @p {Inventory:[{id:"minecraft:writable_book",Damage:0s,Count:1b,Slot:0b}]}

Slot:0 is your first hotbar slot

Still doesn't work 😞

Please recheck in 14w07a since MC-47212 was fixed.