A method of testing the integrity of a filter element in a falter assembly includes a) wetting filter material of a filter element having an inlet side and an outlet side connected to an outlet conduit, b) subjecting the inlet side of the filter element to a gas pressure, c) measuring the pressure in the outlet conduit as a function of time, with a downstream outlet valve for the outlet conduit being closed, and d) determining whether the pressure measured at a preselected time exceeds a reference pressure by a predetermined amount, or determining whether the time required to reach a preselected pressure is shorter than a reference time by a predetermined amount.