diff --git a/.github/workflows/pytest.yml b/.github/workflows/pytest.yml
index fc9af2f..8e67963 100644
--- a/.github/workflows/pytest.yml
+++ b/.github/workflows/pytest.yml
@@ -30,7 +30,7 @@ jobs:
     - name: Lint with flake8
       run: |
         pip install flake8
-        ./flake_check.sh
+        ./flake8.sh
     - name: Test with pytest
       run: |
         pip install pytest
diff --git a/flake_check.sh b/flake8.sh
similarity index 100%
rename from flake_check.sh
rename to flake8.sh
diff --git a/test/test_env.py b/test/test_env.py
new file mode 100644
index 0000000..e56afff
--- /dev/null
+++ b/test/test_env.py
@@ -0,0 +1,57 @@
+import gym
+import time
+import numpy as np
+from tianshou.env import FrameStack, VectorEnv, SubprocVectorEnv, RayVectorEnv
+
+
+class MyTestEnv(gym.Env):
+    def __init__(self, size, sleep=0):
+        self.size = size
+        self.sleep = sleep
+        self.index = 0
+
+    def reset(self):
+        self.index = 0
+        return self.index
+
+    def step(self, action):
+        if self.sleep > 0:
+            time.sleep(self.sleep)
+        if self.index == self.size:
+            return self.index, 0, True, {}
+        if action == 0:
+            self.index = max(self.index - 1, 0)
+            return self.index, 0, False, {}
+        elif action == 1:
+            self.index += 1
+            finished = self.index == self.size
+            return self.index, int(finished), finished, {}
+
+def test_framestack():
+    k = 4
+    size = 10
+    env = MyTestEnv(size=size)
+    fsenv = FrameStack(env, k)
+    fsenv.seed()
+    obs = fsenv.reset()
+    assert abs(obs - np.array([0, 0, 0, 0])).sum() == 0
+    for i in range(5):
+        obs, rew, done, info = fsenv.step(1)
+    assert abs(obs - np.array([2, 3, 4, 5])).sum() == 0
+    for i in range(10):
+        obs, rew, done, info = fsenv.step(0)
+    assert abs(obs - np.array([0, 0, 0, 0])).sum() == 0
+    for i in range(9):
+        obs, rew, done, info = fsenv.step(1)
+    assert abs(obs - np.array([6, 7, 8, 9])).sum() == 0
+    assert (rew, done) == (0, False)
+    obs, rew, done, info = fsenv.step(1)
+    assert abs(obs - np.array([7, 8, 9, 10])).sum() == 0
+    assert (rew, done) == (1, True)
+    obs, rew, done, info = fsenv.step(0)
+    assert abs(obs - np.array([8, 9, 10, 10])).sum() == 0
+    assert (rew, done) == (0, True)
+    fsenv.close()
+
+if __name__ == '__main__':
+    test_framestack()
\ No newline at end of file
diff --git a/tianshou/env/wrapper.py b/tianshou/env/wrapper.py
index c1b0c10..ca81f97 100644
--- a/tianshou/env/wrapper.py
+++ b/tianshou/env/wrapper.py
@@ -50,7 +50,10 @@ class FrameStack(EnvWrapper):
         return self._get_obs()
 
     def _get_obs(self):
-        return np.concatenate(self._frames, axis=-1)
+        try:
+            return np.concatenate(self._frames, axis=-1)
+        except ValueError:
+            return np.stack(self._frames, axis=-1)
 
 
 class VectorEnv(object):
@@ -177,11 +180,10 @@ class RayVectorEnv(object):
         self.env_num = len(env_fns)
         self._reset_after_done = kwargs.get('reset_after_done', False)
         try:
-            import ray
-        except ImportError:
+            if not ray.is_initialized():
+                ray.init()
+        except NameError:
             raise ImportError('Please install ray to support VectorEnv: pip3 install ray -U')
-        if not ray.is_initialized():
-            ray.init()
         self.envs = [ray.remote(EnvWrapper).options(num_cpus=0).remote(e()) for e in env_fns]
 
     def __len__(self):
diff --git a/tianshou/utils/__init__.py b/tianshou/utils/__init__.py
index 128ba80..266c2b2 100644
--- a/tianshou/utils/__init__.py
+++ b/tianshou/utils/__init__.py
@@ -1,3 +1,4 @@
 from tianshou.utils.cloudpicklewrapper import CloudpickleWrapper
+from tianshou.utils.config import tqdm_config
 
-__all__ = ['CloudpickleWrapper']
+__all__ = ['CloudpickleWrapper', 'tqdm_config']
diff --git a/tianshou/utils/config.py b/tianshou/utils/config.py
new file mode 100644
index 0000000..4cf8503
--- /dev/null
+++ b/tianshou/utils/config.py
@@ -0,0 +1,4 @@
+tqdm_config = {
+    'dynamic_ncols': True,
+    'ascii': True,
+}