Taking a look at this guide if you are interested at the details on signing your order requests.
3.0 introduced two new functions: client_api and server_appi as a replacement of old-styled function based api .
3.0 keeps backward compatibility with 2.*, The only thing you should keep in mind is Alipay.verify won't pop sign from data automatically, you should handle it by yourself.
python -m unittest discoverOr you may do test manually in this way, debug=True will direct your request to sandbox environment:
alipay = AliPay(..., debug=True)