This document discusses an automatic test data generation technique that uses particle swarm optimization (PSO) to generate test data that satisfies data flow coverage criteria. PSO is inspired by bird flocking behavior and simulates the movement of particles in a swarm to find the best solution. The PSO algorithm works by having a population of candidate solutions called particles that are moved around in the search space according to rules. The technique was able to automatically generate test data that successfully covered sample programs under all definition-use path criteria and required less generations than genetic algorithms to achieve coverage.