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?

bergercookie · Accepted Answer · 2020-12-11 16:54:44Z

130

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, 2020 at 16:54

bergercookie

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answered May 31, 2013 at 23:44

Simeon Visser

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5 Comments

Naftuli Kay Over a year ago

If I print the value of r.ok from in the method_under_test, I see <MagicMock name='post().ok' id='57360464'>, not True.

Simeon Visser Over a year ago

@TKKocheran: I have updated my answer. You also need to use a PropertyMock.

lumbric Over a year ago

Why not simpy using patched_post.return_value = mock.Mock(ok=True)?

Bono Over a year ago

@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.

chepner Over a year ago

Just because Response.ok is a property doesn't mean the fake response also has to provide a property. The code under test one cares that r.ok evaluates to True or False; how you implement that in the mock shouldn't matter.

Michele d'Amico · Accepted Answer · 2020-10-14 07:18:58Z

27

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, 2020 at 7:18

answered Apr 29, 2015 at 13:12

Michele d'Amico

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Comments

howaryoo · Accepted Answer · 2015-08-31 09:18:52Z

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, 2015 at 9:18

answered Apr 8, 2015 at 9:18

howaryoo

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2 Comments

Michele d'Amico Over a year ago

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.

howaryoo Over a year ago

@Micheled'Amico thanks for your feedback, I tried please take a look ;-)

Lloyd · Accepted Answer · 2024-09-16 21:53:54Z

1

Another alternative using a decorator to mock the attribute

@mock.patch('path.to.your.Object')
def test_object(self, mock_object):
  mock_object.return_value.property_to_mock = 'your mock property value'

edited Sep 16, 2024 at 21:53

answered Aug 27, 2024 at 19:36

Lloyd

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1 Comment

Adam Basha Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

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