Based on a schematic, that is designed for the PCB layout, a simulation can be started. The user adds, if so, a current source or a defined stimulus and points of measurements to the schematic. This methode is similar to a physical test preparation with function generator and oscilloscope.
But PSpice is much more flexible as the measurement on prototypes, because by a mouse click the component parameters can be modified or complete series of different components can be compared in a simulation, without buying or desoldering any samples.
The simulation enables the developer to test also the component tolerances by an extensive experimental serie and to predict with a so called worst-case analyisis the quality of the circuit during the run production.