Is provisional degree certificate valid for applying for UPSC tests?

How will you get Provisional Certificate without completing the course? A Provisional certificate will be given to the candidates who are successful in the final examinations immediately after the declaration of the results. Original certificates will be issued after the convocation only. Till such time, one has to manage with a Provisional certificate only. All government organisations will accept the provisional certificate as proof of educational qualifications. Anyhow you have to attach all the marks lists also with provisional or original certificate.
The university from which you have studied will issue a provisional certificate once you passed the examinations and completed all the formalities to declare that you have passed the examination. But no university will give a provisional certificate without completing your studies and getting passed only.

Yes, provisional certificates are acceptable to show your eligibility criteria for appearing your UPSC examination. However there is a question mark how the same can be obtained without passing the same examination. A provisional certificate is released only after the declaration of the examination. The authorities would accept such a certificate because it provides testimony to the aspirants of having passed their graduation examination. This would be valid in all the circumstances when the aspirants are expecting their original certificates after the convocation ceremony. This is acceptable to all the government organisations including UPSC examination.
In absence of the original certificate, you might send the Xerox copies of your mark sheet of the said examination along with the Xerox copy of the said certificate as a proof of your eligibility for the said examination.
But unless you pass out the same examination, how could be possible for you to have procured the provisional certificate?

Once you qualify in your final examination in that degree then you will be getting a provisional certificate to that extent immediately after the declaration of the results. So there is no problem with that account. There are many examinations in our country where the provisional certificate is given to the students and after some considerable time they get the final certificate for which there could be a convocation function or the student could get it by post. All those students are submitting their provisional certificates only in the places where they are applying for further study or appearing in a competition or applying for a job.
Your provisional certificate will be acceptable by the UPSC time being and later you can submit the original and final one. You can go ahead with your exams and feel free from this botheration.