mocking a socket connection in Python

Question

I am trying to write unit tests for a class in python. The class opens a tcp socket on init. I am trying to mock this out so that I can assert that connecting is called with the correct values but obviously doesn't actually happen in unit tests. I have tired MagicMock, patch, etc but I have not found a solution.

My class so far looks like this

import socket

class MyClass(object):

    def __init__(self):
        self.tcp_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.tcp_socket.connect('0.0.0.0', '6767')

Answer 1

If you just want to assert that connect is called correctly, it's a simple as

import mock
import socket

class MyClass(object):

    def __init__(self):
        self.tcp_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.tcp_socket.connect('0.0.0.0', '6767')

with mock.patch('socket.socket'):
    c = MyClass()
    c.tcp_socket.connect.assert_called_with('0.0.0.0', '6767')

If you have to import a module first to access MyClass, you'll need to adjust the patch slightly:

from mymodule import MyClass
import mock

with mock.patch('mymodule.socket.socket'):
    c = MyClass()
    c.tcp_socket.connect.assert_called_with('0.0.0.0', '6767')