Actually, I have just been puzzled as to what I could possibly offer by way of an answer.
As I understand your query, you are going to be tested for your aptitude. (In American English, you would say that you are going to "sit for" a test or "take" a test. "Write" a test implies that you would be composing a test for someone to use in testing others.)
Having been an RP tech for many years in the past, including a few months at OPG, I really don't know what aptitudes could be tested that would help select RP techs. They didn't give me an aptitude test.
I guess at least a working knowledge of simple algebra would be needed, as well as the ability to measure, calculate, and convert things like area, volume, mass, density, ... etc.
The ability to use a scientific calculator is pretty handy.
Basic logic exercises are probably a good indicator, as RP Techs tend to use procedures a lot. So, I would say that you might run some IF/THEN or WHEN type situations. Most procedures are written that way.
While not absolutely necessary, the ability to read and get information from system diagrams, prints, or engineering drawings is somewhat helpful.
Oh yeah, the ability to communicate a thought by the written word can be valuable too.
Maybe I did have something to add after all, eh?