There are a lot of books with a dedicated chapter on testing, but a book dedicated only on tdd, not really…
I think there is a tdd based development in Phoenix Inside Out, but I did not read it, and maybe someone can confirm.
There is a book dedicated on testing only, it is
But it’s all about property based testing 
which seems to be a new way of testing.
Anyway You will see that testing in a functional world is a breeze (mostly no side effect), and tests are incredibly fast (run concurrently).
