diff --git a/stable_baselines3/common/vec_env/base_vec_env.py b/stable_baselines3/common/vec_env/base_vec_env.py
index ce03391..adf2ec0 100644
--- a/stable_baselines3/common/vec_env/base_vec_env.py
+++ b/stable_baselines3/common/vec_env/base_vec_env.py
@@ -9,7 +9,8 @@ import cloudpickle
 from stable_baselines3.common import logger
 
 
-def tile_images(img_nhwc: Sequence[np.ndarray]) -> np.ndarray:
+
+def tile_images(img_nhwc: Sequence[np.ndarray]) -> np.ndarray:  # pragma: no cover
     """
     Tile N images into one big PxQ image
     (P,Q) are chosen to be as close as possible, and if N
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 9386cb3..5c029ec 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -3,6 +3,7 @@ import shutil
 
 import pytest
 import gym
+import numpy as np
 
 from stable_baselines3 import A2C
 from stable_baselines3.common.monitor import Monitor
@@ -43,14 +44,23 @@ def test_make_vec_env(env_id, n_envs, wrapper_kwargs):
 
     assert env.num_envs == n_envs
 
+    obs = env.reset()
+
+    new_obs, reward, _, _ = env.step([env.action_space.sample() for _ in range(n_envs)])
+
+    assert obs.shape == new_obs.shape
+
+    # Wrapped into DummyVecEnv
     wrapped_atari_env = env.envs[0]
     if wrapper_kwargs is not None:
-        # Wrapped into DummyVecEnv + Monitor
+        assert obs.shape == (n_envs, 60, 60, 1)
         assert wrapped_atari_env.observation_space.shape == (60, 60, 1)
         assert wrapped_atari_env.clip_reward == False
     else:
+        assert obs.shape == (n_envs, 84, 84, 1)
         assert wrapped_atari_env.observation_space.shape == (84, 84, 1)
         assert wrapped_atari_env.clip_reward == True
+        assert np.max(np.abs(reward)) < 1.0