Issue on petting_zoo_api

I get the following error only when i try to use the example for the petting_zoo_api in hello_world_pettingzoo.py :

> Traceback (most recent call last):
> File "/home/dario/Desktop/progetto_RL/MicroRTS-Py/hello_world_pettingzoo.py", line 76, in
> main()
> File "/home/dario/Desktop/progetto_RL/MicroRTS-Py/hello_world_pettingzoo.py", line 51, in main
> env = PettingZooMicroRTSGridModeSharedMemVecEnv(2, 0, ai2s=opponents)
> File "/home/dario/Desktop/progetto_RL/MicroRTS-Py/gym_microrts/petting_zoo_api.py", line 33, in __init__
> super(AECEnv, self).__init__(
> File "/home/dario/Desktop/progetto_RL/MicroRTS-Py/gym_microrts/envs/vec_env.py", line 453, in __init__
> super(MicroRTSGridModeSharedMemVecEnv, self).__init__(
> File "/home/dario/Desktop/progetto_RL/MicroRTS-Py/gym_microrts/envs/vec_env.py", line 144, in __init__
> self.start_client()
> File "/home/dario/Desktop/progetto_RL/MicroRTS-Py/gym_microrts/envs/vec_env.py", line 479, in start_client
> from ts import JNIGridnetSharedMemVecClient as Client
> ImportError: cannot import name 'JNIGridnetSharedMemVecClient' from 'tests' (unknown location)