Abstract: A pressure test cap is provided which positively seals a duct, having a shaped end portion, of a component in preparation for a pressure or leaking test thereof. The test cap has: a sealing cap for enclosing the shaped end portion of the duct, the sealing cap having a portion conforming to the shape of the shaped end portion of the duct; an expansible collet for disposal within the shaped end portion of the duct, the collet having an outer surface conforming with the shape of the shaped end portion of the duct; and an actuator which extends through the sealing cap and engages the collet, expanding the collet radially outwardly so that the shaped end portion of the duct is engaged between the outer surface of the collet and the portion of the sealing cap so that the duct is sealed by said sealing cap, and for contracting the collet radially inwardly so that the sealing cap and the expansible collet may be either removed or mounted upon the duct as may be required.