An apparatus for testing flexible containers traveling along a production line is disclosed. The apparatus includes a compression assembly in line with the production line. The compression assembly has a flexible section for directly contacting and applying a predetermined compression over a predetermined distance to a plurality of containers as they travel by an inspection station. The apparatus also includes a sensor assembly provided in direct contact with a container while a container is in the inspection station. The sensor assembly is arranged to sense the force applied by the compression assembly to the container. The sensor assembly generates a signal that varies in accordance with the internal pressure of the containers as they pass by the sensor assembly. The apparatus further includes a processing circuit configured to receive the signals from the sensor assembly and to determine the acceptability of the internal pressure of the containers.