# FoundationDB Authors - Simulation and Testing (Highlights)  ## Highlights - robust simulation, live performance testing, and hardware-based failure testing. - increased intensity of the failures - a *deterministic* simulation of an entire FoundationDB cluster within a single-threaded process - Determinism is crucial in that it allows perfect repeatability - simulates all physical components - To swizzle-clog, you first pick a random subset of nodes in the cluster. Then, you “clog” (stop) each of their network connections one by one over a few seconds. Finally, you unclog them in a random order, again one by one, until they are all up.