How to assert a monkey patch was called in pytest?

Question

Consider the following:

class MockResponse:
 status_code = 200
 @staticmethod
 def json():
 return {'key': 'value'}
 # where api_session is a fixture
def test_api_session_get(monkeypatch, api_session) -> None:
 def mock_get(*args, **kwargs):
 return MockResponse()
 monkeypatch.setattr(requests.Session, 'get', mock_get)
 response = api_session.get('endpoint/') # My wrapper around requests.Session
 assert response.status_code == 200
 assert response.json() == {'key': 'value'}
 monkeypatch.assert_called_with(
 'endpoint/',
 headers={
 'user-agent': 'blah',
 },
 )

How can I assert that the get I am patching gets called with '/endpoint' and headers? When I run the test now I get the following failure message:

FAILED test/utility/test_api_session.py::test_api_session_get - AttributeError: 'MonkeyPatch' object has no attribute 'assert_called_with'

What am I doing wrong here? Thanks to all those of who reply in advance.

Answer 1

Going to add another response that uses monkeypatch rather than "you can't use monkeypatch"

Since python has closures, here is my poor man's way of doing such things with monkeypatch:

patch_called = False
def _fake_delete(keyname):
 nonlocal patch_called
 patch_called = True
 assert ...
monkeypatch.setattr("mymodule._delete", _fake_delete)
res = client.delete(f"/.../{delmeid}"). # this is a flask client
assert res.status_code == 200
assert patch_called

In your case, since we are doing similar things with patching an HTTP servers method handler, you could do something like (not saying this is pretty):

param_called = None
def _fake_delete(param):
 nonlocal param_called
 patch_called = param
 assert ...
monkeypatch.setattr("mymodule._delete", _fake_delete)
res = client.delete(f"/.../{delmeid}")
assert res.status_code == 200
assert param_called == "whatever this should be"

Answer 2

You need a Mock object to call assert_called_with - monkeypatch does not provide that out of the box. You can use unittest.mock.patch with side_effect instead to achieve this:

from unittest import mock
import requests
...
@mock.patch('requests.Session.get')
def test_api_session_get(mocked, api_session) -> None:
 def mock_get(*args, **kwargs):
 return MockResponse()
 mocked.side_effect = mock_get
 response = api_session.get('endpoint/') 
 ...
 mocked.assert_called_with(
 'endpoint/',
 headers={
 'user-agent': 'blah',
 },
 )

Using side_effect is needed to still get a mock object (mocked in this case, of type MagickMock), instead of just setting your own object in patch, otherwise you won't be able to use the assert_called_... methods.

To clarify: when I write "monkeypatch does not provide that out of the box" this is related to the usage of the assert_called... methods. It does not imply that you can't use monkeypatch to implement a similar functionality, as is nicely shown in the answer by Tommy.