A method for testing an optical assembly (1) which has an optical microstructure (3) integrated with a substrate (2). The optical microstructure (3) is positioned to form an external optical interaction area (4) on a part of a surface (5) of the substrate (2). A cover cap (6) seals at least a part of the surface (5) of the substrate (2) adjacent to the optical microstructure (3) to obtain a sealed cavity (9). An optical feedthrough (10) is integrated in the substrate (2) to form an external communication path from within the sealed cavity (9). The optical feedthrough (10) allows communication of a physical parameter value which is measured inside the sealed cavity (9) to outside the sealed cavity (9). The physical parameter value is associated with a measure of hermeticity of the sealed cavity (9).