def test_make_gym_stack(name, num_envs, state_shape, reward_scale):
    seed = 0
    frame_op = 'stack'  # used for rnn
    frame_op_len = 4
    venv = make_gym_venv(name, num_envs, seed, frame_op=frame_op, frame_op_len=frame_op_len, reward_scale=reward_scale)
    venv.reset()
    for i in range(5):
        state, reward, done, info = venv.step([venv.action_space.sample()] * num_envs)

    assert isinstance(state, np.ndarray)
    stack_shape = (num_envs, frame_op_len,) + state_shape
    assert state.shape == stack_shape
    assert isinstance(reward, np.ndarray)
    assert reward.shape == (num_envs,)
    assert isinstance(done, np.ndarray)
    assert done.shape == (num_envs,)
    assert len(info) == num_envs
    venv.close()