The invention relates to a method for in-process integrity test of a filter. The method may comprise the steps of: coupling a gas source to an input side of a filter (202) without removing the filter from a dispenser system, the gas source supplying a gas (22) and controlling a pressure of the gas coupling a tube (204) to an output side of the filter (202), the tube being filled with a liquid (20): increasing the pressure while monitoring the tube (204), with a light beam (21), for a displacement of the liquid (20) by one or more gas bubbles (23) and determining a value of the pressure at which the displacement of the liquid (20) is detected.
