The ReliaSolve Github page hosts an open-source Arduino-based latency tester project, Latent.  It includes build instructions, Arduino code, and CMake-buildable projects to estimate the input-device latency and motion-to-photon latency for a VR application.

It also includes a CMake-buildable project to estimate the rendering latency (render command to photon) using the Sensics/OSVR RenderManager rendering system.

Latent was used to measure and help minimize the end-to-end system latency within OSVR.