In this paper, we describe an application-level emulator for P2P systems with a special focus on high reproducibility. 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 industrial product. Therefore, we were constrained by the architecture of the overlying application. However, we managed to provide highly transparent emulation by wrapping standard/widely-used networking and concurrency APIs. The resulting environment has proven to be useful in a production 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.