Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Python: unit testing socket-based code?

Tags:

I'm writing a Python client+server that uses gevent.socket for communication. Are there any good ways of testing the socket-level operation of the code (for example, verifying that SSL connections with an invalid certificate will be rejected)? Or is it simplest to just spawn a real server?

Edit: I don't believe that "naive" mocking will be sufficient to test the SSL components because of the complex interactions involved. Am I wrong in that? Or is there a better way to test SSL'd stuff?

like image 817
David Wolever Avatar asked Oct 28 '10 23:10

David Wolever


People also ask

Is Python good for socket programming?

Python provides two levels of access to network services. At a low level, you can access the basic socket support in the underlying operating system, which allows you to implement clients and servers for both connection-oriented and connectionless protocols.

What is Setsockopt Python?

The setsockopt() function provides an application program with the means to control socket behavior. An application program can use setsockopt() to allocate buffer space, control timeouts, or permit socket data broadcasts. The <sys/socket. h> header defines the socket-level options available to setsockopt().


2 Answers

You can easily start a server and then access it in a test case. The gevent's own test suite does exactly that for testing gevent's built-in servers.

For example:

class SimpleServer(gevent.server.StreamServer):

    def handle(self, socket, address):
        socket.sendall('hello and goodbye!')

class Test(unittest.TestCase):      

    def test(self):
        server = SimpleServer(('127.0.0.1', 0))
        server.start()
        client = gevent.socket.create_connection(('127.0.0.1', server.server_port))
        response = client.makefile().read()
        assert response == 'hello and goodbye!'
        server.stop()

Using 0 for the port value means the server will use any available port. After the server is started, the actual value chosen by bind is available as server_port attribute.

StreamServer supports SSL too, pass keyfile and certfile arguments to the constructor and it will wrap each socket with SSLObject before passing it to your handler.

If you don't use StreamServer and your server is based on Greenlet then indeed spawning it is what you should do. Don't forget to kill it at the end of the test case.

Starting a server and spawning a greenlet are fast operations in gevent, much faster than creating a new thread or process and you can easily create a new server for each test case. Just don't forget to cleanup as soon as you don't need the server anymore.

I believe there's no need to mock any of gevent API, it's much easier just to use it as servers and clients can happily live within the same process.

like image 143
Denis Avatar answered Sep 19 '22 18:09

Denis


Mocking and stubbing are great, but sometimes you need to take it up to the next level of integration. Since spawning a server, even a fakeish one, can take some time, consider a separate test suite (call them integration tests) might be in order.

"Test it like you are going to use it" is my guideline, and if you mock and stub so much that your test becomes trivial it's not that useful (though almost any test is better than none). If you are concerned about handling bad SSL certs, by all means make some bad ones and write a test fixture you can feed them to. If that means spawning a server, so be it. Maybe if that bugs you enough it will lead to a refactoring that will make it testable another way.

like image 44
Bill Gribble Avatar answered Sep 20 '22 18:09

Bill Gribble