I completed a reasoning test for job on Sunday (May 16), and was wondering how long it would take for HR to reply? The job offer is new though and only listed since May 9. PS I probably got around ~60% of questions right?
Once you have given your post-interview feedback to the person interviewing you, any further or repeated inquiry will send a message of neediness and desperation.
The time frame you've outlined would dictate that there is a strong possibility that they are still interviewing people, and still compiling a list of more possible candidates. You are unlikely to hear back from them immediately unless you've nailed the interview, to the point of them not wanting to hear from anyone else. Which, from your own assessment of the reasoning test, you did not.
My advice would be to always continue the job hunt until you have an offer; the last thing you want to do is pass up an opportunity because you suspect someone is getting back to you about another. And think of this interview as a learning experience.