In this work we report the results of the testing of an electrochromic window. The test was performed utilizing a special test cell that allows the control of many parameters (temperature, humidity, illumination, etc.) in order to obtain a set of realistic test conditions carefully defining both the indoor and outdoor environments. The cell shows strongly adiabatic behaviour on all the walls except the one holding the tested component. In our case this was an electrochromic window, made of an array of single electrochromic devices, mounted in a wooden frame. The global thermal exchange coefficient, the solar factor, the global and diffused light transmittance, the daylight coefficient were measured in both the optical states (bleached and coloured) in winter and in summer. We also discussed the possibility of automatically controlling the indoor illumination. An estimate of the energy saving is also given.