In this paper we present a system that helps users test their spreadsheets using automatically generated test cases. The system generates the test cases by backward propagation and solution of constraints on cell values. These constraints are obtained from the formula of the cell that is being tested when we try to execute all feasible DU associations within the formula. AutoTest generates test cases that execute all feasible DU pairs. If infeasible DU associations are present in the spreadsheet, the system is capable of detecting and reporting all of these to the user. We also present a comparative evaluation of our approach against the "Help Me Test" mechanism in Forms/3 and show that our approach is faster and produces test suites that give better DU coverage.