During my initial training - which was "old school" and lasted about three years, I would have sat probably 20 exams/tests, both written and oral.
It's an ongoing learning process throughout - and after* - the training.
The final test is made up of a practical, actually doing the job while an examiner watches, and a lengthy and comprehensive oral test.
By the time a candidate is put forward for the final "test", the trainers and management at the unit hosting the candidate should have a very good idea that the candidate will pass.
*every time there is a significant change in procedure, or operating system or similar, there is usually a training course with a test at the culmination. Sometimes this takes the form of computer based training (or, death by powerpoint), and sometimes a proper course that may include simulator training and instruction. Every year there is a cyclical training session lasting two days designed to cover rarely used procedures or upcoming or past changes to tech, law, procedures etc.