Herein disclosed is an x-ray florescence (XRF) test system which comprises an XRF test instrument used for testing a test target's responses to X-rays, the instrument including a test window allowing the X-ray and its responsive energy to pass through, and a window protecting film assembly allowing X-rays to pass through and providing protection to the window, the film assembly being configured to be coupled with the window in a fashion to be removed from or applied or reapplied over the window. The corresponding calibration mode can be manually or automatically applied according to the specific film assembly presently in use. An embodiment of the film assembly comprises a thin film fixed with an adhesive layer to a supporting frame having a closely spaced array of apertures.