@Override
            public void update(float tpf){
                if (state == 0){
                    flash.emitAllParticles();
                    spark.emitAllParticles();
                    smoketrail.emitAllParticles();
                    debris.emitAllParticles();
                    shockwave.emitAllParticles();
                    state++;
                }
                if (state == 1){
                    flame.emitAllParticles();
                    roundspark.emitAllParticles();
                    state++;
                }
            }
This test's particle effects (using an explosion)
jme3-screenshot-tests/src/test/java/org/jmonkeyengine/screenshottests/effects/TestExplosionEffect.java