No way around doing some kind of real-world test. Every Raptor engine does get test fired before being installed on the full vehicle, so it’s unlikely the engines are outright defective. More likely is that there’s some systemic problem, whether related to the complicated plumbing, or the fact that there are 32 other engines in the vicinity, or the launch mount (which is actually an extended part of the engines), or something ellse. All things where computer modeling only gets you so far.
They have been doing some interesting testing on the Raptors. For instance, here’s where they have the engine pointed 15 degrees up:
Normally, if your engine is pointed that way, you will not go to space today. But it’s a legitimate configuration when the upper stage is doing its bellyflop maneuver (horizontal ship with full gimbal deflection on the engine).