Test refactoring (#2427)

* Move tests to root with automatic PyCharm import refactoring. This will likely fail some tests

* Changed entry point for a registration test env.

* Move a stray lunar_lander test to tests/envs/...

* black

* Change the version from which importlib_metadata is replaced with importlib.metadata. Also requiring installing importlib_metadata for python 3.8 now.

???????????

* Undo last commit

tests/wrappers/test_frame_stack.py

@@ -0,0 +1,50 @@
+import pytest
+
+pytest.importorskip("gym.envs.atari")
+
+import numpy as np
+import gym
+from gym.wrappers import FrameStack
+
+try:
+    import lz4
+except ImportError:
+    lz4 = None
+
+
+@pytest.mark.parametrize("env_id", ["CartPole-v1", "Pendulum-v1", "Pong-v0"])
+@pytest.mark.parametrize("num_stack", [2, 3, 4])
+@pytest.mark.parametrize(
+    "lz4_compress",
+    [
+        pytest.param(
+            True,
+            marks=pytest.mark.skipif(
+                lz4 is None, reason="Need lz4 to run tests with compression"
+            ),
+        ),
+        False,
+    ],
+)
+def test_frame_stack(env_id, num_stack, lz4_compress):
+    env = gym.make(env_id)
+    env.seed(0)
+    shape = env.observation_space.shape
+    env = FrameStack(env, num_stack, lz4_compress)
+    assert env.observation_space.shape == (num_stack,) + shape
+    assert env.observation_space.dtype == env.env.observation_space.dtype
+
+    dup = gym.make(env_id)
+    dup.seed(0)
+
+    obs = env.reset()
+    dup_obs = dup.reset()
+    assert np.allclose(obs[-1], dup_obs)
+
+    for _ in range(num_stack ** 2):
+        action = env.action_space.sample()
+        dup_obs, _, _, _ = dup.step(action)
+        obs, _, _, _ = env.step(action)
+        assert np.allclose(obs[-1], dup_obs)
+
+    assert len(obs) == num_stack