We address the problem of testing digital shapers used for nuclear spectroscopy. Particularly, we propose a solution based on the oscillation-based test (OBT) for testing the finite impulse response (FIR) Filters of the shaper. The OBT strategy developed here exploits the natural partition of the system in high-pass and low-pass sections for implementing two different non-linear oscillators. The oscillation parameters are obtained in advance using two different approaches: one based on the filter signal flow-graph; the other based oil the describing function technique. The fault simulation results show high fault coverage and acceptable test time. Additionally, we suggest the use of this test strategy in a BIST environment, because it does not need resources for pattern generation and presents both low system intrusion and low hardware overhead.