A method of testing a tester, comprising testing electronic units using a plurality of sites in order to obtain first bin assignment, instructing the tester to perform a tester quality test if conditions CiQA,1 and CiQA,2 are met, the tester quality test comprising performing a second plurality of tests on an electronic unit using a first site, thereby obtaining second bin assignment for the electronic unit, the second bin assignment being representative of passing or failing of the electronic unit of the second plurality of tests with respect to at least one second test criteria, wherein CiQA,1 is met if passing first bin assignment has been obtained for said electronic unit connected to the tester using the first site, and wherein CiQA,2 is met if data representative of passing first bin assignment obtained for electronic units which have been tested on the first site, meets a quality criteria.