All optical systems in ITER will be based on metallic mirrors. The mirrors, as plasma-facing components, may undergo erosion and re-deposition processes [1] which may influence their optical properties, i.e. reflectivity, which would have a negative impact on spectroscopy signals [2,3]. Tests of first mirrors have therefore been initiated at several machines [4-6], including JET [4] and TCV where dedicated programme has been performed in which small mirror samples are exposed to a variety of divertor plasma configurations. The aim of this paper is to give a brief overview of the tests planned at JET and the experiments underway on TCV.