test_vec_envs.py

import collections
import functools
import itertools
import multiprocessing
import os
import warnings
from typing import Optional

import gymnasium as gym
import numpy as np
import pytest
from gymnasium import spaces

from stable_baselines3 import PPO
from stable_baselines3.common.env_util import make_vec_env
from stable_baselines3.common.monitor import Monitor
from stable_baselines3.common.vec_env import DummyVecEnv, SubprocVecEnv, VecFrameStack, VecNormalize, VecVideoRecorder

try:
    import moviepy  # noqa: F401

    have_moviepy = True
except ImportError:
    have_moviepy = False

N_ENVS = 3
VEC_ENV_CLASSES = [DummyVecEnv, SubprocVecEnv]
VEC_ENV_WRAPPERS = [None, VecNormalize, VecFrameStack]


class CustomGymEnv(gym.Env):
    def __init__(self, space, render_mode: str = "rgb_array"):
        """
        Custom gym environment for testing purposes
        """
        self.action_space = space
        self.observation_space = space
        self.current_step = 0
        self.ep_length = 4
        self.render_mode = render_mode
        self.current_options: Optional[dict] = None

    def reset(self, *, seed: Optional[int] = None, options: Optional[dict] = None):
        if seed is not None:
            self.seed(seed)
        self.current_step = 0
        self.current_options = options
        self._choose_next_state()
        return self.state, {}

    def step(self, action):
        reward = float(np.random.rand())
        self._choose_next_state()
        self.current_step += 1
        terminated = False
        truncated = self.current_step >= self.ep_length
        return self.state, reward, terminated, truncated, {}

    def _choose_next_state(self):
        self.state = self.observation_space.sample()

    def render(self):
        if self.render_mode == "rgb_array":
            return np.zeros((4, 4, 3))

    def seed(self, seed=None):
        if seed is not None:
            np.random.seed(seed)
            self.observation_space.seed(seed)

    @staticmethod
    def custom_method(dim_0=1, dim_1=1):
        """
        Dummy method to test call to custom method
        from VecEnv

        :param dim_0: (int)
        :param dim_1: (int)
        :return: (np.ndarray)
        """
        return np.ones((dim_0, dim_1))


def test_vecenv_func_checker():
    """The functions in ``env_fns'' must return distinct instances since we need distinct environments."""
    env = CustomGymEnv(spaces.Box(low=np.zeros(2), high=np.ones(2)))

    with pytest.raises(ValueError):
        DummyVecEnv([lambda: env for _ in range(N_ENVS)])

    env.close()


@pytest.mark.parametrize("vec_env_class", VEC_ENV_CLASSES)
@pytest.mark.parametrize("vec_env_wrapper", VEC_ENV_WRAPPERS)
def test_vecenv_custom_calls(vec_env_class, vec_env_wrapper):
    """Test access to methods/attributes of vectorized environments"""

    def make_env():
        # Wrap the env to check that get_attr and set_attr are working properly
        return Monitor(CustomGymEnv(spaces.Box(low=np.zeros(2), high=np.ones(2))))

    vec_env = vec_env_class([make_env for _ in range(N_ENVS)])

    if vec_env_wrapper is not None:
        if vec_env_wrapper == VecFrameStack:
            vec_env = vec_env_wrapper(vec_env, n_stack=2)
        else:
            vec_env = vec_env_wrapper(vec_env)

    # Test seed method
    vec_env.seed(0)

    # Test render method call
    array_explicit_mode = vec_env.render(mode="rgb_array")
    # test render without argument (new gym API style)
    array_implicit_mode = vec_env.render()
    assert np.array_equal(array_implicit_mode, array_explicit_mode)

    # test warning if you try different render mode
    with pytest.warns(UserWarning):
        vec_env.render(mode="something_else")

    # we need a X server to test the "human" mode (uses OpenCV)
    # vec_env.render(mode="human")

    # Set a new attribute, on the last wrapper and on the env
    assert not vec_env.has_attr("dummy")
    # Set value for the last wrapper only
    vec_env.set_attr("dummy", 12)
    assert vec_env.get_attr("dummy") == [12] * N_ENVS
    if vec_env_class == DummyVecEnv:
        assert vec_env.envs[0].dummy == 12

    assert not vec_env.has_attr("dummy2")
    # Set the value on the original env
    # Note: doesn't work anymore with gym >= 1.1,
    # the value needs to exists before
    # `set_wrapper_attr` doesn't exist before v1.0
    if gym.__version__ > "1":
        vec_env.env_method("set_wrapper_attr", "dummy2", 2)
        assert vec_env.get_attr("dummy2") == [2] * N_ENVS
        # if vec_env_class == DummyVecEnv:
        #     assert vec_env.envs[0].unwrapped.dummy2 == 2

    env_method_results = vec_env.env_method("custom_method", 1, indices=None, dim_1=2)
    setattr_results = []
    # Set new variable dummy1 of the last wrapper to an arbitrary value
    for env_idx in range(N_ENVS):
        setattr_results.append(vec_env.set_attr("dummy1", env_idx, indices=env_idx))
    # Retrieve the value for each environment
    assert vec_env.has_attr("dummy1")
    getattr_results = vec_env.get_attr("dummy1")

    assert len(env_method_results) == N_ENVS
    assert len(setattr_results) == N_ENVS
    assert len(getattr_results) == N_ENVS

    for env_idx in range(N_ENVS):
        assert (env_method_results[env_idx] == np.ones((1, 2))).all()
        assert setattr_results[env_idx] is None
        assert getattr_results[env_idx] == env_idx

    # Call env_method on a subset of the VecEnv
    env_method_subset = vec_env.env_method("custom_method", 1, indices=[0, 2], dim_1=3)
    assert (env_method_subset[0] == np.ones((1, 3))).all()
    assert (env_method_subset[1] == np.ones((1, 3))).all()
    assert len(env_method_subset) == 2

    # Test to change value for all the environments
    setattr_result = vec_env.set_attr("dummy1", 42, indices=None)
    getattr_result = vec_env.get_attr("dummy1")
    assert setattr_result is None
    assert getattr_result == [42 for _ in range(N_ENVS)]

    # Additional tests for setattr that does not affect all the environments
    vec_env.reset()
    # Since gym >= 0.29, set_attr only sets the attribute on the last wrapper
    # but `set_wrapper_attr` doesn't exist before v1.0
    if gym.__version__ > "1":
        setattr_result = vec_env.env_method("set_wrapper_attr", "current_step", 12, indices=[0, 1])
        getattr_result = vec_env.get_attr("current_step")
        getattr_result_subset = vec_env.get_attr("current_step", indices=[0, 1])
        assert setattr_result == [True, True]
        assert getattr_result == [12 for _ in range(2)] + [0 for _ in range(N_ENVS - 2)]
        assert getattr_result_subset == [12, 12]
        assert vec_env.get_attr("current_step", indices=[0, 2]) == [12, 0]

        vec_env.reset()
        # Change value only for first and last environment
        setattr_result = vec_env.env_method("set_wrapper_attr", "current_step", 12, indices=[0, -1])
        getattr_result = vec_env.get_attr("current_step")
        assert setattr_result == [True, True]
        assert getattr_result == [12] + [0 for _ in range(N_ENVS - 2)] + [12]
        assert vec_env.get_attr("current_step", indices=[-1]) == [12]

    # Checks that options are correctly passed
    assert vec_env.get_attr("current_options")[0] is None
    # Same options for all envs
    options = {"hello": 1}
    vec_env.set_options(options)
    assert vec_env.get_attr("current_options")[0] is None
    # Only effective at reset
    vec_env.reset()
    assert vec_env.get_attr("current_options") == [options] * N_ENVS
    vec_env.reset()
    # Options are reset
    assert vec_env.get_attr("current_options")[0] is None
    # Use a list of options, different for the first env
    options = [{"hello": 1}] * N_ENVS
    options[0] = {"other_option": 2}
    vec_env.set_options(options)
    vec_env.reset()
    assert vec_env.get_attr("current_options") == options

    vec_env.close()


class StepEnv(gym.Env):
    def __init__(self, max_steps):
        """Gym environment for testing that terminal observation is inserted
        correctly."""
        self.action_space = spaces.Discrete(2)
        self.observation_space = spaces.Box(np.array([0]), np.array([999]), dtype="int")
        self.max_steps = max_steps
        self.current_step = 0

    def reset(self, *, seed: Optional[int] = None, options: Optional[dict] = None):
        self.current_step = 0
        return np.array([self.current_step], dtype="int"), {}

    def step(self, action):
        prev_step = self.current_step
        self.current_step += 1
        terminated = False
        truncated = self.current_step >= self.max_steps
        return np.array([prev_step], dtype="int"), 0.0, terminated, truncated, {}


@pytest.mark.parametrize("vec_env_class", VEC_ENV_CLASSES)
@pytest.mark.parametrize("vec_env_wrapper", VEC_ENV_WRAPPERS)
def test_vecenv_terminal_obs(vec_env_class, vec_env_wrapper):
    """Test that 'terminal_observation' gets added to info dict upon
    termination."""
    step_nums = [i + 5 for i in range(N_ENVS)]
    vec_env = vec_env_class([functools.partial(StepEnv, n) for n in step_nums])

    if vec_env_wrapper is not None:
        if vec_env_wrapper == VecFrameStack:
            vec_env = vec_env_wrapper(vec_env, n_stack=2)
        else:
            vec_env = vec_env_wrapper(vec_env)

    zero_acts = np.zeros((N_ENVS,), dtype="int")
    prev_obs_b = vec_env.reset()
    for step_num in range(1, max(step_nums) + 1):
        obs_b, _, done_b, info_b = vec_env.step(zero_acts)
        assert len(obs_b) == N_ENVS
        assert len(done_b) == N_ENVS
        assert len(info_b) == N_ENVS
        env_iter = zip(prev_obs_b, obs_b, done_b, info_b, step_nums)
        for prev_obs, obs, done, info, final_step_num in env_iter:
            assert done == (step_num == final_step_num)
            if not done:
                assert "terminal_observation" not in info
            else:
                terminal_obs = info["terminal_observation"]

                # do some rough ordering checks that should work for all
                # wrappers, including VecNormalize
                assert np.all(prev_obs < terminal_obs)
                assert np.all(obs < prev_obs)

                if not isinstance(vec_env, VecNormalize):
                    # more precise tests that we can't do with VecNormalize
                    # (which changes observation values)
                    assert np.all(prev_obs + 1 == terminal_obs)
                    assert np.all(obs == 0)

        prev_obs_b = obs_b

    vec_env.close()


SPACES = collections.OrderedDict(
    [
        ("discrete", spaces.Discrete(2)),
        ("multidiscrete", spaces.MultiDiscrete([2, 3])),
        ("multibinary", spaces.MultiBinary(3)),
        ("continuous", spaces.Box(low=np.zeros(2, dtype=np.float32), high=np.ones(2, dtype=np.float32))),
    ]
)


def check_vecenv_spaces(vec_env_class, space, obs_assert):
    """Helper method to check observation spaces in vectorized environments."""

    def make_env():
        return CustomGymEnv(space)

    vec_env = vec_env_class([make_env for _ in range(N_ENVS)])
    obs = vec_env.reset()
    obs_assert(obs)

    dones = [False] * N_ENVS
    while not any(dones):
        actions = [vec_env.action_space.sample() for _ in range(N_ENVS)]
        obs, _rews, dones, _infos = vec_env.step(actions)
        obs_assert(obs)
    vec_env.close()


def check_vecenv_obs(obs, space):
    """Helper method to check observations from multiple environments each belong to
    the appropriate observation space."""
    assert obs.shape[0] == N_ENVS
    for value in obs:
        assert space.contains(value)


@pytest.mark.parametrize("vec_env_class,space", itertools.product(VEC_ENV_CLASSES, SPACES.values()))
def test_vecenv_single_space(vec_env_class, space):
    def obs_assert(obs):
        return check_vecenv_obs(obs, space)

    check_vecenv_spaces(vec_env_class, space, obs_assert)


class _UnorderedDictSpace(spaces.Dict):
    """Like DictSpace, but returns an unordered dict when sampling."""

    def sample(self):
        return dict(super().sample())


@pytest.mark.parametrize("vec_env_class", VEC_ENV_CLASSES)
def test_vecenv_dict_spaces(vec_env_class):
    """Test dictionary observation spaces with vectorized environments."""
    space = spaces.Dict(SPACES)

    def obs_assert(obs):
        assert isinstance(obs, dict)
        assert obs.keys() == space.spaces.keys()
        for key, values in obs.items():
            check_vecenv_obs(values, space.spaces[key])

    check_vecenv_spaces(vec_env_class, space, obs_assert)

    unordered_space = _UnorderedDictSpace(SPACES)
    # Check that vec_env_class can accept unordered dict observations (and convert to OrderedDict)
    check_vecenv_spaces(vec_env_class, unordered_space, obs_assert)


@pytest.mark.parametrize("vec_env_class", VEC_ENV_CLASSES)
def test_vecenv_tuple_spaces(vec_env_class):
    """Test tuple observation spaces with vectorized environments."""
    space = spaces.Tuple(tuple(SPACES.values()))

    def obs_assert(obs):
        assert isinstance(obs, tuple)
        assert len(obs) == len(space.spaces)
        for values, inner_space in zip(obs, space.spaces):
            check_vecenv_obs(values, inner_space)

    return check_vecenv_spaces(vec_env_class, space, obs_assert)


def test_subproc_start_method():
    start_methods = [None]
    # Only test thread-safe methods. Others may deadlock tests! (gh/428)
    # Note: adding unsafe `fork` method as we are now using PyTorch
    all_methods = {"forkserver", "spawn", "fork"}
    available_methods = multiprocessing.get_all_start_methods()
    start_methods += list(all_methods.intersection(available_methods))
    space = spaces.Discrete(2)

    def obs_assert(obs):
        return check_vecenv_obs(obs, space)

    for start_method in start_methods:
        vec_env_class = functools.partial(SubprocVecEnv, start_method=start_method)
        check_vecenv_spaces(vec_env_class, space, obs_assert)

    with pytest.raises(ValueError, match="cannot find context for 'illegal_method'"):
        vec_env_class = functools.partial(SubprocVecEnv, start_method="illegal_method")
        check_vecenv_spaces(vec_env_class, space, obs_assert)


class CustomWrapperA(VecNormalize):
    def __init__(self, venv):
        VecNormalize.__init__(self, venv)
        self.var_a = "a"


class CustomWrapperB(VecNormalize):
    def __init__(self, venv):
        VecNormalize.__init__(self, venv)
        self.var_b = "b"

    def func_b(self):
        return self.var_b

    def name_test(self):
        return self.__class__


class CustomWrapperBB(CustomWrapperB):
    def __init__(self, venv):
        CustomWrapperB.__init__(self, venv)
        self.var_bb = "bb"


def test_vecenv_wrapper_getattr():
    def make_env():
        return CustomGymEnv(spaces.Box(low=np.zeros(2), high=np.ones(2)))

    vec_env = DummyVecEnv([make_env for _ in range(N_ENVS)])
    wrapped = CustomWrapperA(CustomWrapperBB(vec_env))
    assert wrapped.var_a == "a"
    assert wrapped.var_b == "b"
    assert wrapped.var_bb == "bb"
    assert wrapped.func_b() == "b"
    assert wrapped.name_test() == CustomWrapperBB

    double_wrapped = CustomWrapperA(CustomWrapperB(wrapped))
    _ = double_wrapped.var_a  # should not raise as it is directly defined here
    with pytest.raises(AttributeError):  # should raise due to ambiguity
        _ = double_wrapped.var_b
    with pytest.raises(AttributeError):  # should raise as does not exist
        _ = double_wrapped.nonexistent_attribute


def test_framestack_vecenv():
    """Test that framestack environment stacks on desired axis"""

    image_space_shape = [12, 8, 3]
    zero_acts = np.zeros([N_ENVS, *image_space_shape])

    transposed_image_space_shape = image_space_shape[::-1]
    transposed_zero_acts = np.zeros([N_ENVS, *transposed_image_space_shape])

    def make_image_env():
        return CustomGymEnv(
            spaces.Box(
                low=np.zeros(image_space_shape),
                high=np.ones(image_space_shape) * 255,
                dtype=np.uint8,
            )
        )

    def make_transposed_image_env():
        return CustomGymEnv(
            spaces.Box(
                low=np.zeros(transposed_image_space_shape),
                high=np.ones(transposed_image_space_shape) * 255,
                dtype=np.uint8,
            )
        )

    def make_non_image_env():
        return CustomGymEnv(spaces.Box(low=np.zeros((2,)), high=np.ones((2,))))

    vec_env = DummyVecEnv([make_image_env for _ in range(N_ENVS)])
    vec_env = VecFrameStack(vec_env, n_stack=2)
    obs, _, _, _ = vec_env.step(zero_acts)
    vec_env.close()

    # Should be stacked on the last dimension
    assert obs.shape[-1] == (image_space_shape[-1] * 2)

    # Try automatic stacking on first dimension now
    vec_env = DummyVecEnv([make_transposed_image_env for _ in range(N_ENVS)])
    vec_env = VecFrameStack(vec_env, n_stack=2)
    obs, _, _, _ = vec_env.step(transposed_zero_acts)
    vec_env.close()

    # Should be stacked on the first dimension (note the transposing in make_transposed_image_env)
    assert obs.shape[1] == (image_space_shape[-1] * 2)

    # Try forcing dimensions
    vec_env = DummyVecEnv([make_image_env for _ in range(N_ENVS)])
    vec_env = VecFrameStack(vec_env, n_stack=2, channels_order="last")
    obs, _, _, _ = vec_env.step(zero_acts)
    vec_env.close()

    # Should be stacked on the last dimension
    assert obs.shape[-1] == (image_space_shape[-1] * 2)

    vec_env = DummyVecEnv([make_image_env for _ in range(N_ENVS)])
    vec_env = VecFrameStack(vec_env, n_stack=2, channels_order="first")
    obs, _, _, _ = vec_env.step(zero_acts)
    vec_env.close()

    # Should be stacked on the first dimension
    assert obs.shape[1] == (image_space_shape[0] * 2)

    # Test invalid channels_order
    vec_env = DummyVecEnv([make_image_env for _ in range(N_ENVS)])
    with pytest.raises(AssertionError):
        vec_env = VecFrameStack(vec_env, n_stack=2, channels_order="not_valid")

    # Test that it works with non-image envs when no channels_order is given
    vec_env = DummyVecEnv([make_non_image_env for _ in range(N_ENVS)])
    vec_env = VecFrameStack(vec_env, n_stack=2)


def test_vec_env_is_wrapped():
    # Test is_wrapped call of subproc workers
    def make_env():
        return CustomGymEnv(spaces.Box(low=np.zeros(2), high=np.ones(2)))

    def make_monitored_env():
        return Monitor(CustomGymEnv(spaces.Box(low=np.zeros(2), high=np.ones(2))))

    # One with monitor, one without
    vec_env = SubprocVecEnv([make_env, make_monitored_env])

    assert vec_env.env_is_wrapped(Monitor) == [False, True]

    vec_env.close()

    # One with monitor, one without
    vec_env = DummyVecEnv([make_env, make_monitored_env])

    assert vec_env.env_is_wrapped(Monitor) == [False, True]

    vec_env = VecFrameStack(vec_env, n_stack=2)
    assert vec_env.env_is_wrapped(Monitor) == [False, True]


@pytest.mark.parametrize("vec_env_class", VEC_ENV_CLASSES)
def test_vec_deterministic(vec_env_class):
    def make_env():
        env = CustomGymEnv(gym.spaces.Box(low=np.zeros(2), high=np.ones(2)))
        return env

    vec_env = vec_env_class([make_env for _ in range(N_ENVS)])
    vec_env.seed(3)
    obs = vec_env.reset()
    vec_env.seed(3)
    new_obs = vec_env.reset()
    assert np.allclose(new_obs, obs)
    # Test with VecNormalize (VecEnvWrapper should call self.venv.seed())
    vec_normalize = VecNormalize(vec_env)
    vec_normalize.seed(3)
    obs = vec_env.reset()
    vec_normalize.seed(3)
    new_obs = vec_env.reset()
    assert np.allclose(new_obs, obs)
    vec_normalize.close()
    # Similar test but with make_vec_env
    vec_env_1 = make_vec_env("Pendulum-v1", n_envs=N_ENVS, vec_env_cls=vec_env_class, seed=0)
    vec_env_2 = make_vec_env("Pendulum-v1", n_envs=N_ENVS, vec_env_cls=vec_env_class, seed=0)
    assert np.allclose(vec_env_1.reset(), vec_env_2.reset())
    random_actions = [vec_env_1.action_space.sample() for _ in range(N_ENVS)]
    assert np.allclose(vec_env_1.step(random_actions)[0], vec_env_2.step(random_actions)[0])
    vec_env_1.close()
    vec_env_2.close()


@pytest.mark.parametrize("vec_env_class", VEC_ENV_CLASSES)
def test_vec_seeding(vec_env_class):
    def make_env():
        return CustomGymEnv(spaces.Box(low=np.zeros(2), high=np.ones(2)))

    # For SubprocVecEnv check for all starting methods
    start_methods = [None]
    if vec_env_class != DummyVecEnv:
        all_methods = {"forkserver", "spawn", "fork"}
        available_methods = multiprocessing.get_all_start_methods()
        start_methods = list(all_methods.intersection(available_methods))

    for start_method in start_methods:
        if start_method is not None:
            vec_env_class = functools.partial(SubprocVecEnv, start_method=start_method)

        n_envs = 3
        vec_env = vec_env_class([make_env] * n_envs)
        # Seed with no argument
        vec_env.seed()
        obs = vec_env.reset()
        _, rewards, _, _ = vec_env.step(np.array([vec_env.action_space.sample() for _ in range(n_envs)]))
        # Seed should be different per process
        assert not np.allclose(obs[0], obs[1])
        assert not np.allclose(rewards[0], rewards[1])
        assert not np.allclose(obs[1], obs[2])
        assert not np.allclose(rewards[1], rewards[2])

        vec_env.close()


@pytest.mark.parametrize("vec_env_class", VEC_ENV_CLASSES)
def test_render(vec_env_class):
    # Skip if no X-Server
    if not os.environ.get("DISPLAY"):
        pytest.skip("No X-Server")

    env_id = "Pendulum-v1"
    # DummyVecEnv human render is currently
    # buggy because of gym:
    # https://github.com/carlosluis/stable-baselines3/pull/3#issuecomment-1356863808
    n_envs = 2
    # Human render
    vec_env = make_vec_env(
        env_id,
        n_envs,
        vec_env_cls=vec_env_class,
        env_kwargs=dict(render_mode="human"),
    )

    vec_env.reset()
    vec_env.render()

    with pytest.warns(UserWarning):
        vec_env.render("rgb_array")

    with pytest.warns(UserWarning):
        vec_env.render(mode="blah")

    for _ in range(10):
        vec_env.step([vec_env.action_space.sample() for _ in range(n_envs)])
        vec_env.render()

    vec_env.close()
    # rgb_array render, which allows human_render
    # thanks to OpenCV
    vec_env = make_vec_env(
        env_id,
        n_envs,
        vec_env_cls=vec_env_class,
        env_kwargs=dict(render_mode="rgb_array"),
    )

    vec_env.reset()
    with warnings.catch_warnings(record=True) as record:
        vec_env.render()
        vec_env.render("rgb_array")
        vec_env.render(mode="human")

    # No warnings for using human mode
    assert len(record) == 0

    with pytest.warns(UserWarning):
        vec_env.render(mode="blah")

    for _ in range(10):
        vec_env.step([vec_env.action_space.sample() for _ in range(n_envs)])
        vec_env.render()

    # Check that it still works with vec env wrapper
    vec_env = VecFrameStack(vec_env, 2)
    vec_env.render()
    assert vec_env.render_mode == "rgb_array"
    vec_env = VecNormalize(vec_env)
    assert vec_env.render_mode == "rgb_array"
    vec_env.render()

    vec_env.close()


@pytest.mark.skipif(not have_moviepy, reason="moviepy is not installed")
def test_video_recorder(tmp_path):
    env_id = "CartPole-v1"
    video_folder = str(tmp_path)

    vec_env = make_vec_env(env_id, n_envs=1)

    # Wrap to check unwrapping works
    vec_env = VecNormalize(vec_env)

    # Record the video starting at the first step
    vec_env = VecVideoRecorder(
        vec_env,
        video_folder,
        record_video_trigger=lambda x: x % 65 == 0,
        video_length=10,
        name_prefix=f"agent-{env_id}",
    )

    model = PPO("MlpPolicy", vec_env, n_steps=64, n_epochs=1, verbose=0)

    model.learn(total_timesteps=128)

    # print all videos in video_folder, should be multiple step 0-100, step 1024-1124
    video_files = list(map(str, tmp_path.glob("*.mp4")))
    video_files.sort(reverse=True)

    # Clean up
    vec_env.close()

    assert len(video_files) == 2
    assert "agent-CartPole-v1-step-65-to-step-75.mp4" in video_files[0]
    assert "agent-CartPole-v1-step-0-to-step-10.mp4" in video_files[1]