added assertion of 'NoFrameskip' in AtariPreprocessing (#1725)

* added assertion of noframeskip in atari pre-proecessing

* - corrected frameskipping assertion
- added non-op assertion as well

gym/wrappers/atari_preprocessing.py

@@ -40,7 +40,10 @@ class AtariPreprocessing(gym.Wrapper):
         super().__init__(env)
         assert frame_skip > 0
         assert screen_size > 0
-
+        assert noop_max >= 0
+        if frame_skip > 1:
+            assert 'NoFrameskip' in env.spec.id, 'disable frame-skipping in the original env. for more than one' \
+                                                 ' frame-skip as it will be done by the wrapper'
         self.noop_max = noop_max
         assert env.unwrapped.get_action_meanings()[0] == 'NOOP'
 

gym/wrappers/test_gray_scale_observation.py

@@ -8,7 +8,7 @@ from gym.wrappers import AtariPreprocessing
 pytest.importorskip('atari_py')
 pytest.importorskip('cv2')
 
-@pytest.mark.parametrize('env_id', ['Pong-v0', 'SpaceInvaders-v0'])
+@pytest.mark.parametrize('env_id', ['PongNoFrameskip-v0', 'SpaceInvadersNoFrameskip-v0'])
 @pytest.mark.parametrize('keep_dim', [True, False])
 def test_gray_scale_observation(env_id, keep_dim):
     gray_env = AtariPreprocessing(gym.make(env_id), screen_size=84, grayscale_obs=True)

gym/wrappers/test_resize_observation.py

@@ -9,7 +9,7 @@ except ImportError:
 
 
 @pytest.mark.skipif(atari_py is None, reason='Only run this test when atari_py is installed')
-@pytest.mark.parametrize('env_id', ['Pong-v0', 'SpaceInvaders-v0'])
+@pytest.mark.parametrize('env_id', ['PongNoFrameskip-v0', 'SpaceInvadersNoFrameskip-v0'])
 @pytest.mark.parametrize('shape', [16, 32, (8, 5), [10, 7]])
 def test_resize_observation(env_id, shape):
     env = gym.make(env_id)