Recent advances in test automation have seen a host of new techniques for automated test generation, which traditionally has largely been a manual and expensive process. These techniques have enabled generation of much larger numbers of tests at a much reduced cost. When executed successfully, these tests enable a significant increase in our confidence in the program's correctness. However, as our ability to generate greater numbers of tests increases, we are faced with the problem of the likely high cost of executing all the tests in terms of the total execution time. This thesis presents a novel approach - clustered test execution - to address this problem. Instead of executing each test case separately, we execute parts of several tests using a single execution, which then forks into several directions as the behaviors of the tests differ. Our insight is that in a large test suite, several tests are likely to have common initial execution segments, which do not have to be executed over and over again; rather such a segment could be executed once and the execution result shared across all those tests. As an enabling technology we use the Java PathFinder(JPF) model checker, which is a popular explicit-state model checker for Java programs. Experimental results show that our clustering approach for test execution using JPF provides speed-ups over executing each test in turn from a test suite on the JPF java virtual machine. / text