Through-Silicon Vias (TSVs) enable high-density, low-latency, and low-power interconnects for system chips that consist of multiple dies. In "2.5D" Stacked ICs (2.5D-SICs), multiple dies without TSVs are stacked side-by-side on top of a passive silicon interposer base containing TSVs. In true 3D-SICs, multiple dies containing TSVs themselves are vertically stacked; one or multiple of such stacks are possibly placed on a passive silicon interposer. This paper proposes a post-bond test and design-for-test (DfT) strategy for 2.5D- and 3D-SICs containing a passive silicon interposer base. Functional interconnects in the interposer are reused as much as possible in order to keep the interposer cost low.