diff --git a/.github/workflows/pytest.yml b/.github/workflows/pytest.yml
index 91789db..1715738 100644
--- a/.github/workflows/pytest.yml
+++ b/.github/workflows/pytest.yml
@@ -30,7 +30,10 @@ jobs:
     - name: Lint with flake8
       run: |
         pip install flake8
-        ./flake8.sh
+        # stop the build if there are Python syntax errors or undefined names
+        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+        # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
+        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
     - name: Test with pytest
       run: |
         pip install pytest pytest-cov
diff --git a/setup.py b/setup.py
index 96f325f..87f41ce 100644
--- a/setup.py
+++ b/setup.py
@@ -32,6 +32,7 @@ setup(
         # that you indicate whether you support Python 2, Python 3 or both.
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
     ],
     keywords='reinforcement learning platform',
     # You can just specify the packages manually here if your project is
diff --git a/test/__init__.py b/test/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/test/test_buffer.py b/test/test_buffer.py
new file mode 100644
index 0000000..ea6c9b2
--- /dev/null
+++ b/test/test_buffer.py
@@ -0,0 +1,19 @@
+from tianshou.data import ReplayBuffer
+from test.test_env import MyTestEnv
+
+
+def test_replaybuffer(bufsize=20):
+    env = MyTestEnv(10)
+    buf = ReplayBuffer(bufsize)
+    obs = env.reset()
+    action_list = [1] * 5 + [0] * 10 + [1] * 9
+    for i, a in enumerate(action_list):
+        obs_next, rew, done, info = env.step(a)
+        buf.add(obs, a, rew, done, obs_next, info)
+        assert len(buf) == min(bufsize, i + 1), print(len(buf), i)
+    indice = buf.sample_indice(4)
+    data = buf.sample(4)
+
+
+if __name__ == '__main__':
+    test_replaybuffer()
\ No newline at end of file
diff --git a/test/test_env.py b/test/test_env.py
index 1c9cea1..67912e0 100644
--- a/test/test_env.py
+++ b/test/test_env.py
@@ -80,6 +80,8 @@ def test_vecenv(verbose=False, size=10, num=8, sleep=0.001):
                 e.step([a] * num)
             t[i] = time.time() - t[i]
         print(f'VectorEnv: {t[0]:.6f}s\nSubprocVectorEnv: {t[1]:.6f}s\nRayVectorEnv: {t[2]:.6f}s')
+    for v in venv:
+        v.close()
 
 
 if __name__ == '__main__':
diff --git a/tianshou/data/batch.py b/tianshou/data/batch.py
index 937afa6..ee16eb0 100644
--- a/tianshou/data/batch.py
+++ b/tianshou/data/batch.py
@@ -1,6 +1,5 @@
 class Batch(object):
     """Suggested keys: [obs, act, rew, done, obs_next, info]"""
-
     def __init__(self, **kwargs):
         super().__init__()
         self.__dict__.update(kwargs)
diff --git a/tianshou/data/buffer.py b/tianshou/data/buffer.py
index d294ae7..20e66d3 100644
--- a/tianshou/data/buffer.py
+++ b/tianshou/data/buffer.py
@@ -7,7 +7,7 @@ class ReplayBuffer(object):
     def __init__(self, size):
         super().__init__()
         self._maxsize = size
-        self._index = self._size = 0
+        self.reset()
 
     def __len__(self):
         return self._size
@@ -45,7 +45,7 @@ class ReplayBuffer(object):
         return np.random.choice(self._size, batch_size)
 
     def sample(self, batch_size):
-        indice = self.sample_index(batch_size)
+        indice = self.sample_indice(batch_size)
         return Batch(
             obs=self.obs[indice],
             act=self.act[indice],