A medium- or high-voltage switch (10), comprising a high-vacuum enclosure (111); first and second contacts (121, 122) that are mounted to be movable in translation relative to each other inside the enclosure (111) between an open position in which the first and second contacts (121, 122) are spaced apart; and a closed position in which the first and second contacts (121, 122) are in electrical contact. The switch (10) further comprises a conductor (210, 220, 230) arranged inside the enclosure (111) in such a manner that there exists a pressure threshold inside the enclosure (111) from which partial discharges are generated by said conductor, at least when the first and second contacts (121, 122) are in the closed position and the medium or high voltage is applied to the switch (10). The invention further relates to a switch assembly and to a method of testing such a switch.