The number of tests you give for UPSC matters less than how well you analyse them. For Prelims, 25–40 full-length papers are usually sufficient if reviewed properly. For Mains, regular answer writing practice is more important than sheer volume.

Instead of chasing numbers, focus on quality. After every paper, spend time identifying conceptual gaps, repeated mistakes, and weak areas. Improvement comes from analysis, not just attempts.
In the final months before the exam, simulate real conditions to build stamina and decision-making ability. A limited but well-analysed set of tests will help far more than excessive, poorly reviewed ones.