The aptitude tests at Shearwater are virtually the same as those utilised by NATS, and as were used by SERCo at Bailbrook.
At a former company where I was on the management side, (thankfully I saw the light and got back into a proper job
), we used to send ab initio candidates to CATC / Bailbrook, and subsequently Shearwater, for assesments.
In almost all cases, if the candidate was successful on the assesment, they would pass the course.
However, and it's a very
big however, this didn't always mean that the candidate would make it to validation level as an atco.
I seem to remember approximately 30% of candidates not validating and going on to do non atc jobs, sometimes within aviation, sometimes not.
I accept that this also meant that 70% did make it, but you must be aware that the assesment is only the beginning of a very hard couple of years.
Just out of interest, are you paying for the assesment, or is your employer, and if you pass, who will be paying for the course. I only ask in case you're not aware of the possible financial implications.