Increased focus on the Universal Serial Bus (USB) attack surface of devices has recently resulted in a number of new vulnerabilities. Much of this advance has been aided by the advent of hardware-based USB emulation techniques. However, existing tools and methods are far from ideal, requiring a significant investment of time, money, and effort. In this work, we present a USB testing framework that improves significantly over existing methods in providing a cost-effective and flexible way to read and modify USB communication. Amongst other benefits, the framework enables man-in-the-middle fuzz testing between a host and peripheral. We achieve this by performing two-way emulation using inexpensive bespoke USB testing hardware, thereby delivering capabilities of a USB analyzer at a tenth of the cost. Mutation fuzzing is applied during live communication between a host and peripheral, yielding new security-relevant bugs. Lastly, we comment on the potential of the framework to improve current exploitation techniques on the USB channel.