I can't speak for your area but would advise you to get a doctor's note ASAP and withdraw the child from the test if illness continues or occurs. They must offer alternative tests in such cases.
Please do not do what someone did in our area a couple of years ago. They took the vomming child to sit the test - it had been ill during the night and again on the way to the test but the parent inexplicably attributed this to nerves. It vomited during the test, loudly and generously, into a waste bin in the classroom. The parent appealed on the grounds of illness when the child was unsuccessful in the test, but I don't know the outcome. What I do know is that the other children in the room, who had to witness the sights, sounds and odours of the scenario, did not get any special consideration.
Hope all is well and your child stays bug-free though.