Abstract: The invention pertains to a method to test the polishing of a mirror by means of a testing device, in a fluid through which rays of light are propagated homogeneously, and a system that puts this method into use. The method consists in placing the mirror on a support, in fixing this support imperviously to one end of a flexibly shaped and/or folding chamber in such a way that its internal volume can be elminated, the testing device being at an opposite end of the chamber, and it further consists in driving out the residual air contained in the chamber is driven out by eliminating its internal volume, then in injecting a volume of fluid into the chamber so that the polishing can be tested, the said testing being done before the support and the mirror are removed in order to correct faults or to finally package the mirror.