Hmm, are they really testing the theory? Or are they simulating it?
IIRC, the results they got were in agreement with the Dirac equation.
In a way you could say they are "simulating" it, but only in the sense that they are using a different set up, but one which is described by the same equiations. The "solution" on that "analog" exhibits the real physical behavior of the original. So yes they are testing the theory. But not quite the original prediction.
Another way of looking at what they did is to look at their experimental set up as an analog computer which solves the same Dirac equation, suitably scaled I'm sure, as the original near light speed particle behavior. So the only question would be, does the Dirac equation properly describe the original situation.