It started six years ago when some colleagues spent half a man year on debugging a single "simple" bug. The main problem was that this bug appeared very rarely and was therefore very hard to locate. This frustration led to a technology called ConTest whose aim is to make intermittent bugs more likely to appear and to be able to repeat execution that exhibit these bugs. The talk starts by presenting the difficulties of testing multi-threaded programs and showing typical timing related bugs. We then show how to find such bugs. We start by presenting the common concurrent bug patterns and how to use them. Then explain about review for concurrent bugs. The concepts of ConTest - an application that makes the discovery of such bugs easier by changing the relative timing of the threads - is presented. Next we demonstrate how ConTest is used and some of its useful features.