A voltage island architecture wherein the source voltage of each voltage island can be independently turned on/off or adjusted during a scan-based test. The architecture includes a plurality of voltage islands (102, 104), each powered by a respective island source voltage (VDDI1, VDDI2), and a testing circuit (116), coupled to the voltage islands, and powered by a global source voltage (Vg) that is always on during test, wherein each island source voltage may be independently controlled (106, 108) during test.