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.

What do you have so far?

Mahmoud Abdelkader
– Mahmoud Abdelkader

2011-03-16 00:33:07 +00:00
Commented Mar 16, 2011 at 0:33 — Mahmoud Abdelkader
– Mahmoud Abdelkader, Commented Mar 16, 2011 at 0:33

Mahmoud Abdelkader · Accepted Answer · 2011-03-16 00:38:53Z

3

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)

answered Mar 16, 2011 at 0:38

Mahmoud Abdelkader

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3 Comments

Renne Rocha Over a year ago

I didn't understand the patch decorator before. After your answer, I read again the mock documentation and see that is the better way (or the only one :-) ) to accomplish what I need.

Renne Rocha Over a year ago

Unfortunately the patch decorater is ok if I am trying to change the return of some function of Session class. But if I try to change the data dictionary, the test result in: TypeError: 'Mock' object is not subscriptable

Mahmoud Abdelkader Over a year ago

@Renne your question is unclear. What are you trying to do exactly? Can you please post a snippet that demonstrates your problem? Also, your question, thusly, changes from its original form.

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