def METHOD_NAME(self):
    prob = om.Problem()
    prob.model.add_subsystem('double', VectorDoublingComp(size=3))  # 'size' is an option
    prob.setup()
    prob.set_val('double.x', [1., 2., 3.])
    prob.run_model()
    assert_near_equal(prob.get_val('double.y'), [2., 4., 6.])