A set of techniques includes devices, methods, and user interfaces, capable of conducting proactive automated tests of a wireless system, and capable of operating while the wireless system is conducting its normal operations. A diagnostic device not controlled by the wireless system controls drivers and clients in that wireless system's access points, with the effect that the diagnostic device can inject message traffic into the wireless system while simulating clients of that system. The wireless system responds to that traffic and those simulated clients as if real clients were generating substantially real traffic for the system to handle. The diagnostic device can initiate messages from within that wireless system, can force those messages to traverse selected trajectories in that system, and can measure aspects of that system in response to those messages. Trajectories might include specific wireless devices, specific wireless parameters, and specific physical paths.