An opto-electronic assembly and testing method are disclosed. A housing of the opto-electronic assembly is coupled to a window to form an optical chamber. A retro-reflector can be coupled to the housing. A radiation source can be disposed on or about the retro-reflector. The radiation source can emit radiation into the optical chamber through at least a portion of the retro-reflector. A detector can sense a level of the radiation in the optical chamber. A controller coupled to the detector can signal an error condition when the level of the radiation exceeds a threshold associated with the presence of obscurants on the window. Optionally, the controller can be coupled to the radiation source for selectively emitting pulses of radiation into the optical chamber and detecting data bits corresponding to the pulses of radiation.