Mazda’s next-generation MX-5 has been spied undergoing testing at the Nurburgring, Germany. The prototype sports a heavily-modified MX-5 body which has been pieced together. The test vehicle gives us an idea of the next roadster's overall dimensions.Image gallery: Mazda MX-5NEXT MAZDA ROADSTERDetails are hard to make out but you can spot an added section in front of the A-pillar which suggests the model will have classic "long hood, short deck" proportions. The vehicle has longer doors, which implies it has a longer wheelbase. The extended wheel arches suggests the roadster could have a wider track.Engine options have yet to be confirmed but the automaker has previously said its next MX-5 will be powered by a specific proprietary engine. Early speculation suggests the MX-5 will use either a 1.3- or 1.6-litre SkyActiv engine. The new model is expected to be launched in 2015.