Is it considered a sin if you see someone cheating on an exam and do not report it to the teacher, and what if you fear the consequences of doing so, such as failing the exam, or being killed or beaten?

Cheating is forbidden, and remaining silent about it, when one is able to denounce it, is also forbidden. Therefore, it is obligatory to advise the cheater and warn him. "Whoever cheats is not one of us," and it is not permissible to cooperate in sin and aggression. "Whoever among you sees an evil, let him change it." Advice is obligatory to the extent of one's ability, as long as the advisor does not fear harm to himself. If a person fears that his words will not be heeded, he can inform the supervisor to change the evil by preventing its occurrence, unless he fears harm to himself or the occurrence of a greater mischief. If he fears harm, then we hope that there will be nothing held against him, based on the saying of the Prophet, peace and blessings be upon him: "Indeed, Allah will question His servant on the Day of Resurrection until He says: 'What prevented you, when you saw the evil, from denouncing it?' So, if Allah prompts a servant with his argument, he will say: 'My Lord, I hoped in You and I feared people.'"