[QUESTION] How to test BackgroundTasks?

I’m wondering if there is a recommended way to stub out BackgroundTasks in unit tests? If I’m running a test for an endpoint I definitely don’t want to run any BackgroundTasks that endpoint is creating (e.g. sending emails).

The way I’m doing this right now which seems to work is by creating a wrapper dependency so I can then override it like any other custom dependency. Like this:

def tasks(background_tasks: BackgroundTasks) -> BackgroundTasks:
    """ Just a wrapper dependency for BackgroundTasks """
    return background_tasks

@router.post("/")
def my_endpoint(background_tasks: BackgroundTasks = Depends(tasks)):
    tasks.add_task(...)

Then in my conftest.py I do something like:

@pytest.fixture
def mock_backround_tasks(mocker):
    """ The mocked background_tasks dependency """
    return mocker.MagicMock(autospec=BackgroundTasks)

app.dependency_overrides[tasks] = lambda: mock_backround_tasks

This feels a bit clunky, I’m wondering if there is a better way to do something like this and if you might add a Testing BackgroundTasks section to the docs with your recommendation?

[Kludex]

In case people want an example:

    with patch("fastapi.BackgroundTasks.add_task") as mock:

        def side_effect(*args, **kwargs):
            <do something>

        mock.side_effect = side_effect

[mateoradman]

In addition to the comments above, it is also possible to modify the behaviour of a particular background task using the built-in pytest fixture monkeypatch.

def do_nothing(*_: list[Any]) -> None:
    return None

@pytest.mark.anyio
async def test_create_something(
    monkeypatch,
    async_client: AsyncClient,
    db: Session,
) -> None:
    monkeypatch.setattr("app.background_tasks.handle_uploaded_file", do_nothing)  # make the background_task do_nothing
    r = await async_client.post(
        ....
    )
    assert r.status_code == 201