PHP Interview Assessment

PHP Interview Assessment

I need advice on building out a 15-20 minute PHP Assessment for an early
stage of my recruiting funnel. For full disclosure I'm not a technical
person, I'm a founder that really puts a lot of emphasis on hiring.
I'm in the process of revamping our entire interview process for our
junior developers. One thing that's correlated really highly to job
performance has been an early-stage assessment of the job seekers skills.
We're hiring so many junior programmers (0-3 yrs of experience) that this
is the only way to really understand what they know.
The goal is to build out a 15-20 minute (10-12 question) PHP Test. It
can't be over 20 minutes since I'm using this early in the recruitment
process (after the candidates apply).
There are two things I need:
CONTENT, PHP Questions that actually test BROAD concepts. I want this to
weed-out the guys that absolutely know nothing about PHP.
In order to steamline the process I'm putting all of this into an online
testing platform and each candidate will have an overall raw score for the
hiring manager. The content must be shaped into multiple choice questions
with an answer.
I found this site that's interesting: http://pskills.org/php.jsp
I'm not a technical person so are these PHP questions good enough to test
candidates who state "I know PHP" on their resume? Recommendations or
Advice on how to build something better?