Statistical tests are very important tools to study the variability of Active Galactic Nuclei (AGNs). There are many statistical tests like C-test, F-test, scaled-F-test, enhanced-F-test, chi-square test etc which is used to classify the variability of AGN. In our talk, I will discuss the advantages and drawbacks of these tests and finally focus on the best test out of these, which is being used vigorously. I will also match our observations with these tests.