All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
In general, this type of test is intended to determine the level of ability the student possesses to derive answers from texts of an open-book and the extent of his ability to find the correct answer.
If he copied the answer from his classmates, then he would deceive the teachers who will correct the test as they will think that he had found the answer with his own effort.
If this is the case, it is not permissible to copy the answer from classmates because that is cheating.
For more benefit that cheating in exams is absolutely prohibited in Islam, please refer to Fataawa 187023, 81709, 86185, 213922 and 344767.
Allah knows best.