Mock attributes in Python mock?

Question

I'm having a fairly difficult time using mock in Python:

def method_under_test():
    r = requests.post("http://localhost/post")

    print r.ok # prints "<MagicMock name='post().ok' id='11111111'>"

    if r.ok:
       return StartResult()
    else:
       raise Exception()

class MethodUnderTestTest(TestCase):

    def test_method_under_test(self):
        with patch('requests.post') as patched_post:
            patched_post.return_value.ok = True

            result = method_under_test()

            self.assertEqual(type(result), StartResult,
                "Failed to return a StartResult.")

The test actually returns the right value, but r.ok is a Mock object, not True. How do you mock attributes in Python's mock library?

score 128 · Accepted Answer · edited Dec 11 '20 at 16:54

128

You need to use return_value and PropertyMock:

with patch('requests.post') as patched_post:
    type(patched_post.return_value).ok = PropertyMock(return_value=True)

This means: when calling requests.post, on the return value of that call, set a PropertyMock for the property ok to return the value True.

edited Dec 11 '20 at 16:54

bergercookie

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answered May 31 '13 at 23:44

Simeon Visser

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If I `print` the value of `r.ok` from in the `method_under_test`, I see ``, not `True`. – Naftuli Kay May 31 '13 at 23:46
@TKKocheran: I have updated my answer. You also need to use a `PropertyMock`. – Simeon Visser May 31 '13 at 23:50
21

Why not simpy using `patched_post.return_value = mock.Mock(ok=True)`? – lumbric Nov 24 '16 at 09:58
4

@lumbric Because you can use `PropertyMock` to assert that it was accessed like any other `Mock` object. By just assigning a value to the property you can't do that. – Bono Mar 15 '18 at 10:32

Michele d'Amico · Answer 2 · 2020-10-14T07:18:58.847

24

A compact and simple way to do it is to use new_callable patch's attribute to force patch to use PropertyMock instead of MagicMock to create the mock object. The other arguments passed to patch will be used to create PropertyMock object.

with patch('requests.post.ok', new_callable=PropertyMock, return_value=True) as mock_post:
    """Your test"""

edited Oct 14 '20 at 07:18

answered Apr 29 '15 at 13:12

Michele d'Amico

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howaryoo · Answer 3 · 2015-08-31T09:18:52.980

22

With mock version '1.0.1' the simpler syntax mentioned in the question is supported and works as is!

Example code updated (py.test is used instead of unittest):

import mock
import requests


def method_under_test():
    r = requests.post("http://localhost/post")

    print r.ok

    if r.ok:
        return r.ok
    else:
        raise Exception()


def test_method_under_test():
    with mock.patch('requests.post') as patched_post:
        patched_post.return_value.ok = True

        result = method_under_test()
        assert result is True, "mock ok failed"

Run this code with: (make sure you install pytest)

$ py.test -s -v mock_attributes.py 
======= test session starts =======================
platform linux2 -- Python 2.7.10 -- py-1.4.30 -- pytest-2.7.2 -- /home/developer/miniconda/bin/python
rootdir: /home/developer/projects/learn/scripts/misc, inifile: 
plugins: httpbin, cov
collected 1 items 

mock_attributes.py::test_method_under_test True
PASSED

======= 1 passed in 0.03 seconds =================

edited Aug 31 '15 at 09:18

answered Apr 08 '15 at 09:18

howaryoo

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This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient [reputation](http://stackoverflow.com/help/whats-reputation) you will be able to [comment on any post](http://stackoverflow.com/help/privileges/comment). – philant Apr 08 '15 at 10:22
FYI `requests.post.ok` is a property and not an attribute. If you try on simple object where `ok` is a simple attribute the *syntax mentioned in the question works* but for `requests.post.ok` object no: it will raise an `AttributeError`. – Michele d'Amico Apr 08 '15 at 10:49
@philant thanks for your feedback, as proved by the example this is the up-to-date answer to the question and the syntax happens to be much simpler. – howaryoo Aug 31 '15 at 09:22
@Micheled'Amico thanks for your feedback, I tried please take a look ;-) – howaryoo Aug 31 '15 at 09:26

Mock attributes in Python mock?

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