String theory
The allegation that string theory makes no testable predictions is false, as it makes many.  No theory—a predictive and perhaps explanatory model of some domain of natural phenomena—is verifiable.  All conventional physical theories until the Standard Model have made claims about unobservable aspects of the natural world.  Even the Standard Model has various interpretations as to the natural world.  When the Standard Model is operated, it is often made a version with supersymmetry, doubling the number of particle species so far identified by particle physicists.