Testing method for establishing a specific material property of a test specimen - using the test specimen of an elongate specimen of a fibre-reinforced plastics material composite of a rotor blade of a wind turbine, wherein the test specimen has a length along a longitudinal axis and a cross-section having a width and a thickness in a transverse axis and wherein the test specimen has the fibre-reinforced plastics material composite and an inner core, wherein - the specific material property of the fibre-reinforced plastics material composite is established, that is to say, by a mechanical, static or dynamic load of a tensile load and/or pressure load along the longitudinal axis of the test specimen engaging in a fixing device of a testing device in a measurement on the test specimen and the specific material property being established, wherein - the inner core is introduced into a composite with the fibre-reinforced plastics material composite, characterised in that, - as a result of the inner core in the transverse axis with respect to the mechanical load, the cross-section of the specimen is expanded in such a manner that the composite with the inner core has a higher resistance to kinking than a composite without the inner core, wherein - the test specimen can be described with a substantially rectangular, elongate specimen geometry and the specimen geometry has an outer dimension with a thickness of at least 0.5 cm, a width of at least 2 cm and a length of at least 20 cm, and - the fibre reinforced plastics material composite has at least one strain gauge, and - the inner core is constructed in such a manner that an influence on the specific material property of the fibre-reinforced plastics material composite which is intended to be established is so low that the material property which is intended to be associated with the core is located within a measurement error range of the measurement for the specific material property, wherein the cross-section of the specimen is expanded in the range of the maximum load application in the centre of the specimen, and the specimen geometry has ends which taper into a face and which are adapted in accordance with the fixing device. - using the test specimen of an elongate specimen of a fibre-reinforced plastics material composite of a rotor blade of a wind turbine, wherein the test specimen has a length along a longitudinal axis and a cross-section having a width and a thickness in a transverse axis and wherein the test specimen has the fibre-reinforced plastics material composite and an inner core, wherein - the specific material property of the fibre-reinforced plastics material composite is established, that is to say, by a mechanical, static or dynamic load of a tensile load and/or pressure load along the longitudinal axis of the test specimen engaging in a fixing device of a testing device in a measurement on the test specimen and the specific material property being established, wherein - the inner core is introduced into a composite with the fibre-reinforced plastics material composite, characterised in that, - as a result of the inner core in the transverse axis with respect to the mechanical load, the cross-section of the specimen is expanded in such a manner that the composite with the inner core has a higher resistance to kinking than a composite without the inner core, wherein - the test specimen can be described with a substantially rectangular, elongate specimen geometry and the specimen geometry has an outer dimension with a thickness of at least 0.5 cm, a width of at least 2 cm and a length of at least 20 cm, and - the fibre reinforced plastics material composite has at least one strain gauge, and - the inner core is constructed in such a manner that an influence on the specific material property of the fibre-reinforced plastics material composite which is intended to be established is so low that the material property which is intended to be associated with the core is located within a measurement error range of the measurement for the specific material property, wherein the cross-section of the specimen is expanded in the range of the maximum load application in the centre of the specimen, and the specimen geometry has ends which taper into a face and which are adapted in accordance with the fixing device.