I did the assessment 2 weeks ago approx. About 60% passed on my day.
ATPL knowledge was very random, some more difficult questions but no calculations necessary. I was unsure of about 20 out of 60 questions, I did not get a low score on these.
For preparation with Skytest i'd say it's very hard to prepare for many of the parts, the best I'd recommend is:
- Multitasking with callsign
- Rotating cube
- Memorize type of aircraft
- Perception test
- Visual memory test
- Shapes puzzle
- General mental math practice
You also get a link to a site with sample tests from them once you are invited, these are very easy though. The real test is more difficult.