Just as Einstein developed a test using a Solar eclipse for his theory
I don't think that Einstein developed the test although he suggested to turn to astronomy for a test. It took an Eddington to design and conduct the experiment from Eddington's understanding of the published theory. It also took some political maneuvers by Dyson to keep Eddington out of the draft so he could do the experiment.
Ludwig Silberstei said Eddington was one of only three men that understood the theory at the time.
It takes a theory, someone who understands it enough to conduct a proper experiment, and someone to finance and support the work. The problem is that is no theory out that is "understandable". Most avoid the conservation of spin, or momentum, or why there is no detectable radiation, or other important physical points. They are not self consistent.