We describe ConTest, a tool for detecting synchronization faults in multithreaded Java[TM] programs. The program under test is seeded with a sleep(), yield(), or priority() primitive at shared memory accesses and synchronization events. At run time, Con Test makes random or coverage-based decisions as to whether the seeded primitive is to be executed. Thus, the probability of finding concurrent faults is increased. A replay algorithm facilitates debugging by saving the order of shared memory ...