In 2000, information system may not operate because in the early of computer age most of hardware and software were designed to recognize last two digit of date. To prevent these disaster, all date related data have to be corrected before 2000. Test in Y2K bug resolution perform to find and to correct errors. But test that is made up above half in Y2K readiness has difficulty due to cost and time constraints. Profound and broad effect of Y2K problem, efficient test methods and criteria are needed. In this paper, some method and criteria are proposed. If program reliability through test is a standard, partition test that uses pre-information about errors has good performance. And economic model that includes error correcting cost and opportunity cost can be used determination of optimal test time that maximize the effect of test.
