Part of the point of a jury is to have multiple disinterested individuals ruling on the defendant's guilt. That in itself forms a partial test of the process.

Part of the point of a jury is to have multiple disinterested individuals ruling on the defendant's guilt. That in itself forms a partial test of the process. You could run a trial with multiple independent juries, or record a trial and play it back to a set of juries and judges to see if they come up with the same verdict and sentence. This would help determine whether a given jury has a particularly forceful and prejudiced member, or if a hanging judge is handing out unfair sentences. I'd be surprised if that sort of thing doesn't already happen occasionally. However, all this does is indicate where a problem might be, rather than validate a potential solution. A/B testing of potential enhancements would be very difficult and limited. There are too many confounding factors. Judge and jury would have to be different each time. Witness testimony may seem unconvincingly rehearsed, or more convincingly thorough, the nth time they give it. Defendants will be able to avoid incriminating traps the prosecuting barrister set in previous iterations of the trial.