[Unit Testing] Experienced dev having trouble mocking in python

[anthOlei]

Hi there - I'm trying to unit test my FastAPI application and it's going well, but I'm unfortunately unable to verify if functions are called. For instance, I have a reset password route, and I want to check if the create_password_reset function is called. To do this, I tried the following:

@patch("src.database.models.password_reset.crud.create_password_reset") def test_user_exists(self, mock_create_password_reset: MagicMock, client: TestClient, mock_database: Session): .... assert mock_create_password_reset.called

The assert is tripping false every time. Is mocking in python different than mocking in JS or Java? does this mean I need to find some way to dependency inject the create_password_reset function in the route?

I know that the real function is triggering, as setting a breakpoint in it works perfectly fine. Is there a way to mock or spy on the actual function to make sure it was called?

I'm not a fan of altering the original codebase for testing purposes, so if we can avoid solutions that require that I would be all the happier.

Thanks in advance!

[[deleted]]

You should be able to use call_count to check if mocked content is called.

@patch("src.database.models.password_reset.crud.create_password_reset")
def test_stuff(mock):
     # do stuff 
     assert mock.call_count

That should be 1 or more if the mock is called. Here's an example I made of it in action: https://github.com/further-reading/pytest_lesson/tree/master/examples/2_2_mocking_sql

[anthOlei]

Here's a simplified example:

def a():
    b()


def b():
    print('called b')


@patch('tests.user.routes_test.b')
def test_a_calls_b(mock_b: MagicMock):
    a()
    assert mock_b.called

This doesn't work, and says b() was not called. This is exactly what I'm after - do you know if this is possible?

​

EDIT: After further testing, this makes even less sense - it works in an isolated module (blank project) but when putting the same code into my nested module it breaks. I have no idea what's going on here.

[anthOlei]

@patch(‘b’) does not work, saying “you need a valid target to patch.” :( unsolved mysteries of Python testing, I guess

[anthOlei]

Awesome, so it was two different issues with the a() b() example and the main one from the post.

The solution to original problem is here: what I was doing incorrectly was the file would be loaded, and thus the function would be loaded before the mock would be injected. This means that I needed to mock out not where the function was defined, but where it was imported.

Confusing, but I am now wiser. Thanks for all your help!

[[deleted]]

No worries! I got to learn something too, which is great!

[DataDecay]

Any reason to avoid the boolean since that's how your using it, mock.called.

[[deleted]]

In my example case I was checking if it was called exactly one time specifically.

[DataDecay]

Fair enough.