Wearing a hijab is not a taboo. The issue is if dress like a ninja in exams room, or prepare a biometric picture, you may not show part of face which will authenticate your document. In the exams room someone can impersonate you that's is the matter. Christians do not have problem with any one wearing a hijab and of our mother Mary her is always picture as wearing a hijab. Carry your trouble and don't make it look as if Christians hate people wearing hijab. I beg your pardon.