<p>This paper presents a new experimental test to characterize the transition between in-plane (Mode II) and out-of-plane (Mode III) shear fractures in sheet-bulk forming processes. Although these two fracture modes have been studied separately, the transition between them remains insufficiently understood and has not yet been directly addressed through a dedicated experimental approach. To achieve this, the authors designed a new sheet-compression formability test based on existing specimen concepts used to independently assess each fracture mode. The geometry of the new sheet-compression test specimen was optimized through finite element modelling, then manufactured and tested using a dedicated setup. Crack initiation was analysed using finite elements and validated by scanning electron microscopy. Strain loading paths were obtained using digital image correlation and mapped into the effective strain vs. stress triaxiality space to evaluate the influence of the stress state on failure. Experimental results supported by finite element analysis show that the new proposed sheet compression formability test successfully produces pure Mode II, pure Mode III, and mixed-mode fractures, depending on the specimen geometry. The originality of this work consists in the development of a single, versatile sheet-compression formability test that combines a dedicated specimen geometry with an adapted tooling configuration. In this unified specimen-fixture configuration, the initial ligament angle controls the transition between pure Mode II, mixed Mode II-Mode III, and pure Mode III shear fracture, providing a practical tool for studying shear-dominated fracture behaviour in sheet-bulk forming processes.</p>