Research and literature on concurrency testing and concurrent testing typically focuses on testing software and systems that use concurrent computing. The purpose is, as with most software testing, to understand the behaviour and performance of a software system that uses concurrent computing, particularly assessing the stability of a system or application during normal activity. Research and literature on concurrency testing and concurrent testing typically focuses on testing software and systems that use concurrent computing. The purpose is, as with most software testing, to understand the behaviour and performance of a software system that uses concurrent computing, particularly assessing the stability of a system or application during normal activity. Research and study of program concurrency started in the 1950’s, with research and study of testing program concurrency appearing in the 1960’s. Examples of problems that concurrency testing might expose are incorrect shared memory access and unexpected order sequence of message or thread execution.:2 Resource contention resolution, scheduling, deadlock avoidance, priority inversion and race conditions are also highlighted.:745 Approaches to concurrency testing may be on a limited unit test level right up to system test level.