Python: block network connections for testing purposes?

Question

I\'m trying to test a package that provides interfaces to a few web services. It has a test suite that is supposed to test most functions without connecting to the

Answer 1

Building on the very helpful answers from Thomas Orozco and driftcatcher here is a variant that works with Python's unittest and (after a small change) Django.

All you need to do is inherit your test case class from the enhanced NoSocketTestCase class and any access to the network will be detected and raises the SocketAccessError exception.

And this approach also works with Django. You only need to change the NoSocketTestCase class to inherit from django.test.TestCase instead of unittest.TestCase.

While not strictly answering OP's question I think this might be helpful for anyone who wants to block network access in unit tests.

no_sockets.py

import socket
from unittest import TestCase


class SocketAccessError(Exception):
    pass


class NoSocketsTestCase(TestCase):
    """Enhancement of TestCase class that prevents any use of sockets

    Will throw the exception SocketAccessError when any code tries to
    access network sockets
    """

    @classmethod
    def setUpClass(cls):
        cls.socket_original = socket.socket
        socket.socket = cls.guard
        return super().setUpClass()

    @classmethod
    def tearDownClass(cls):
        socket.socket = cls.socket_original
        return super().tearDownClass()

    @staticmethod
    def guard(*args, **kwargs):
        raise SocketAccessError('Attempted to access network')

test_no_sockets.py

import urllib.request
from .no_sockets import NoSocketsTestCase, SocketAccessError


class TestNoSocketsTestCase(NoSocketsTestCase):

    def test_raises_exception_on_attempted_network_access(self):

        with self.assertRaises(SocketAccessError):            
            urllib.request.urlopen('https://www.google.com')