the best thing to do is call the embassy as the test he should do is KET (ket english test) as its the easiest.
there is a july exam being held worldwide and i think its happening in tunis (even tho its not on the website) but it looks like the closing date for registration is tomorrow but you might be lucky. the next one might be november or december.
the exam costs 120 dinar and they have to register in person.
as i said i would call them - they are open til 8pn thursdays!
hope this helps