How to mock external authentication decorator used along with routes

[David-Vithayathil]

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Example Code

# project_name/routes/school_routes.py
from external_library import authentication

@router.get("/", status_code=status.HTTP_200_OK, tags=["schools"])
@authentication
def list_schools(request: Request):
  #Code logic

# tests/routes.py
client = TestClient(app)

class TestRoutes(unittest.TestCase):
  @patch('project_name.routes.school_routes.authentication')
  def setUp(self, mock_auth):
     mock_auth.return_value = lambda func: func

  def test_list_schools(self):
     response = client.get(<PATH>)

Description

I am importing this authentication decorator from an external library. I am currently writing unittests for the application and somehow the authentication decorator doesn't get patched.

I am aware of using authentication through Depends() but somehow I am not permitted to alter the authentication decorator as it is commonly used in several other projects primarily written using other frameworks within the org.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.110.3

Pydantic Version

2.7.1

Python Version

3.10

Additional Context

No response

[aanchlia]

Have you tried using patch? Something like this below.

import unittest
from unittest.mock import patch

patcher = patch('project_name.routes.school_routes.authentication')
self.mock_auth = patcher.start()

[David-Vithayathil]

Yes. I've used the patch decorator. The call is still going to the original authentication decorator and not the patched one.

[YuriiMotov]

You can't patch decorator since Python applies decorators right after you import the module and before methods of TestRoutes are called.
So, at the moment when you call TestRoutes's methods, list_schools is already modified and patching the authentication function doesn't have any effect.

Your case is a clear example of the benefits of using dependencies instead of other mechanisms (injecting logic via middlewares, decorators, etc..).

I think you can overcome this by introducing a dependency like it's shown above:

# project_name/routes/school_routes.py
from external_library import authentication

@authentication
def authenticate(request: Request):
    pass

@router.get("/", status_code=status.HTTP_200_OK, tags=["schools"], dependencies=[Depends(authenticate)])
def list_schools():
  #Code logic

To mock the authentication just override the dependency:

def mock_authenticate():
    pass

app.dependency_overrides[authenticate] = mock_authenticate

[David-Vithayathil]

Thanks a lot. I've tried implementing it as you mentioned and it works !!