Whatever it is that you are trying to test, I would first simulate it first. If you want to make it simple, start with simulating the system in the open-loop configuration (without a feedback controller). To do this, apply a gating signal to the switching device by using a pulse source with appropriate duty ratio and frequency. You can use this simulation to estimate the maximum voltages and currents in the transistor, diode, etc. Do the simulation over min/max input voltage and min/max load current to determine the "four corners" of the design.
This would be my answer to your question; however, keith1200rs gave the more correct answer to your question by asking you to clarify your inquiry.
v_c