A method of testing leakage and/or strength of paperboard-based containers, characterised by the steps of: - producing a sealed paperboard-based container; - producing a through-opening in a panel (12, 14, 18) of the container; and - attaching a nozzle to the through-opening; which method further comprises performing at least one of a first series of steps and a second series of steps, wherein the first series of steps comprises: - increasing pressure in the container by injecting a gaseous fluid into the container via the nozzle until a predetermined, first pressure value (p 1) is obtained in the container; - when the first pressure value (p 1) is obtained in the container, closing the nozzle preventing gaseous fluid from entering or exiting the container via the nozzle; - at a predetermined period of time (t wait) after closure of the nozzle, measuring a second pressure value (p 2) in the container; and - using a difference in pressure (p drop) between the first pressure value (p 1) and the second pressure value (p 2) as a measure of leakage of the container, and wherein the second series of steps comprises: - increasing pressure in the container by injecting a gaseous fluid into the container via the nozzle until the container fails; - measuring the maximum pressure value (p max) obtained in the container prior to the container failing; and - using the maximum pressure value (p max) as a measure of the strength of the container, wherein the step of attaching the nozzle to the through-opening comprises the sub-steps of: - inserting a flexible sealing disk encircling a distal end of the nozzle into the container via the through-opening; and - bringing the sealing disk into gas-tight engagement with an inner surface section of the container encircling the through-opening. - producing a sealed paperboard-based container; - producing a through-opening in a panel (12, 14, 18) of the container; and - attaching a nozzle to the through-opening; which method further comprises performing at least one of a first series of steps and a second series of steps, wherein the first series of steps comprises: - increasing pressure in the container by injecting a gaseous fluid into the container via the nozzle until a predetermined, first pressure value (p 1) is obtained in the container; - when the first pressure value (p 1) is obtained in the container, closing the nozzle preventing gaseous fluid from entering or exiting the container via the nozzle; - at a predetermined period of time (t wait) after closure of the nozzle, measuring a second pressure value (p 2) in the container; and - using a difference in pressure (p drop) between the first pressure value (p 1) and the second pressure value (p 2) as a measure of leakage of the container, - increasing pressure in the container by injecting a gaseous fluid into the container via the nozzle until a predetermined, first pressure value (p 1) is obtained in the container; - when the first pressure value (p 1) is obtained in the container, closing the nozzle preventing gaseous fluid from entering or exiting the container via the nozzle; - at a predetermined period of time (t wait) after closure of the nozzle, measuring a second pressure value (p 2) in the container; and - using a difference in pressure (p drop) between the first pressure value (p 1) and the second pressure value (p 2) as a measure of leakage of the container, and wherein the second series of steps comprises: - increasing pressure in the container by injecting a gaseous fluid into the container via the nozzle until the container fails; - measuring the maximum pressure value (p max) obtained in the container prior to the container failing; and - using the maximum pressure value (p max) as a measure of the strength of the container, - increasing pressure in the container by injecting a gaseous fluid into the container via the nozzle until the container fails; - measuring the maximum pressure value (p max) obtained in the container prior to the container failing; and - using the maximum pressure value (p max) as a measure of the strength of the container, wherein the step of attaching the nozzle to the through-opening comprises the sub-steps of: - inserting a flexible sealing disk encircling a distal end of the nozzle into the container via the through-opening; and - bringing the sealing disk into gas-tight engagement with an inner surface section of the container encircling the through-opening. - inserting a flexible sealing disk encircling a distal end of the nozzle into the container via the through-opening; and - bringing the sealing disk into gas-tight engagement with an inner surface section of the container encircling the through-opening.