Be careful
I did the NTR assessment 4 years ago for a job based in Izmir or Antalya.
I was offered a job, but on reading the contract, it said that my base would be Ankara, and any months of my 3 year contract that I didn't fulfill, I would owe them the proposed salary for those months (yes, as in +£200k). It was kind of hidden away too in the small print. I rang HR, who confirmed it, said there was no way to change it, but would offer me a 2 year contract instead.
Not sure if it's still the same, but if you get a job offer, read the contract 10 times before you sign it. Especially the part about leaving early.
For the tests, make sure you do ALL the practice sessions they give you access to. I didn't have a great 'maths' test, but they commented that they were pleased that I had done all of the practicing.
Cheers and good luck.