By combining modern surface strain measurement techniques with the traditional tensile test mechanical test, a method has been developed whereby the mechanical properties of a test sample with a heterogeneous microstructure such can be characterised in one test. In this paper the applicability to such a method of two such surface strain measurement techniques, image correlation (IC) and electronic speckle pattern interferometry (ESPI), is assessed. Two commercially available systems were used to monitor, simultaneously, the surface strain on tensile test specimens during testing. Measurements on homogeneous samples were compared with measurements made using strain gauges and excellent agreement was found. Elastic modulus and proof stress values measured in these standard samples showed that the uncertainty in the measurements was below 10%. The method was then applied to an inertia friction weld, whose strength varied linearly as a function of distance from the weld line. The values of proof stress obtained were compared with micro-hardness measurements.