I want to have a testfor command that only teleports a person with a writable_book with a message, and on a certain team

What you are looking for looks something like this:

{Inventory:[{id:minecraft:written_book,tag:{pages:[0:"\"Test\""]}}]}

But the teleport command does not support NBT tags. However, there is a workaround using scoreboards.

First add a scoreboard objective:

/scoreboard objectives add HoldingBook dummy HoldingBook

Then run these 2 commands on a fast clock:

/scoreboard players set @a HoldingBook 2 {Inventory:[{id:minecraft:written_book,tag:{pages:[0:"\"Test\""]}}]}
/scoreboard players remove @a HoldingBook 1

Now, you can teleport the players holing a written book with the word "Test" on the first page, and for example on team blue;

/tp @a[score_holdingbook_min=1,team=blue] <your-coords>

Hope this helps.