If it's an ordinary college exam, you don't need to show your degree certificate to enter the examination room. Basically, you can rely on your student ID card or admission ticket.
You don't need to provide a degree certificate if you need to take a postgraduate exam during your college years. You just need to get a degree certificate before you enter the graduate school.
If you are a graduate student who graduated from a university, you can also take the exam as long as you have a nationally recognized undergraduate degree (Xuexin.com certification).