In this paper, we describe an application-level emulator for P2P systems with a special focus on high reproducibil-ity. We achieve reproduciblity by taking control over the scheduling of concurrent events from the operating system. We accomplish that for inter- and intra- peer concurrency. The development of the system was driven by the need to enhance the testing process of an already-developed indus-trial product. Therefore, we were constrained by the ar-chitecture of the overlying application. However, we man-aged to provide highly transparent emulation by wrapping standard/widely-used networking and concurrency APIs. The resulting environment has proven to be useful in a pro-duction environment. At this stage, it started to be general enough to be used in the testing process of applications other than the one it was created to test.