1. A method for generating test vectors in cyber-physical systems, comprising: generating traces of a system model or program of a mixed-discrete-continuous system stored in memory using a simulation engine; globally optimizing simulated inputs using a fitness objective computed using a computer processing device, the simulation inputs being sampled in regions of state-space and being adjusted in accordance with feedback from the traces and fitness objective values by computing a distance between the fitness objective value and a reachability objective; and outputting test input vectors based upon optimized fitness objective values associated with the simulated inputs to test the system model or program stored in memory.