1. A method for performing a regression session when testing an electronic system device under test (DUT), the method comprising: using a processor: a. obtaining a coverage model of the DUT, and a verification session input file (VSIF) relating to each test of a plurality of tests to be run on the DUT, the VSIF including an initial number of runs associated with each test of the plurality of tests; b. performing a first iteration of the regression session in which each test of the plurality of tests is run, with a random seed, the initial number of runs associated with said each test; c. calculating an effectiveness grade for each test of the plurality of tests, the calculating including determining a number of coverage points of the coverage model that are covered by each run of said each test and comparing the determined number with the number of coverage points that were covered in runs of said each test previous to said each run, and assigning a weight to each test of the plurality of tests corresponding to the calculated effectiveness grade of said each test; d. iteratively performing further iterations of the regression session in each of which each of the tests of the plurality of tests is run, with a random seed, a number of runs corresponding to the weight assigned to that test in a previous iteration; and calculating for each iteration of the further iterations a new effectiveness grade for each test of the tests of the plurality of tests, and assigning a new weight to each of the test of the plurality of tests, wherein the new effectiveness grade and the new weight are used as the effectiveness grade and the weight, respectively, in a consecutive iteration of the iteratively performed further iterations.