Microsoft USB Test Tool (MUTT) is a suite of physical test devices and an accompanying software package used by hardware test engineers to validate the interoperability and behavior of USB host controllers, hubs, and related firmware with the Microsoft USB driver stack on Windows. The MUTT system includes different hardware variants (e.g., MUTT, MUTT Pack, SuperMUTT, SuperMUTT Pack) that can simulate USB 2.0 and USB 3.x traffic patterns and hub topologies, and is used to run stress, transfer, and power state tests against USB subsystems.