Mocking chained calls in Python

Question

I am trying to test the following class using unittest and the mock library:

class Connection(object):
    def __init__(self, cookie):
    self.connect = None
    self.session = Session()
    self.session.load(cookie)
    # do some stuff with self.session
    self.some_info = self.session.data['the_info']

How could I test if when I create an instance of Connection, depending on the return of the Session instance, I assert if self.some_info is with the value I am expecting?

I wish to use the mock library. In its documentation I have an example of mocking chained calls (http://www.voidspace.org.uk/python/mock/examples.html#mocking-chained-calls), but it isn't very clear of how I can adapt it to my problem.

The Session.load(cookie) method sets some attributes in the Session instance. I would like to set this values fixed for my tests for every value of cookie.

Answer 1

Assume Connection is located in module package.module.connection

The following code should be how you would test your session:

import mock


class TestConnection(unittest.TestCase):

    @mock.patch('package.module.connection.Session')
    def test_some_info_on_session_is_set(self, fake_session):
        fake_session.data = {'the_info': 'blahblah'}
        cookie = Cookie()
        connection = Connection(cookie)
        self.assertEqual(connection.some_info, 'blahblah')
        fake_session.load.assert_called_once_with(cookie)