As `get_db()` is a normal `def` function, **FastAPI** will make it run in a threadpool, with a *copy* of the "context", holding the same value for the context variable (the `dict` with the reset database state). Then it can add database state to that `dict`, like the connection, etc.

    Si tienes bastante conocimiento técnico (coroutines, threads, bloqueos, etc.) y tienes curiosidad acerca de cómo FastAPI gestiona `async def` vs `def` normal, continúa.

### Path operation functions

    data: List[int] = Depends(get_data),
):
    return {"user": user_data[0], "scopes": user_data[1], "data": data}


client = TestClient(app)


def test_normal():
    response = client.get("/user")
    assert response.json() == {
        "user": "john",
        "scopes": ["foo", "bar"],
        "data": [1, 2, 3],
    }


def test_override_data():

## HTTPX

Even if your **FastAPI** application uses normal `def` functions instead of `async def`, it is still an `async` application underneath.

    assert response.status_code == 200, response.text
    assert response.json() == {
        "message": "Hello Users!",
        "params": {"q": "foo", "skip": 5, "limit": 10},
    }


def test_normal_app():
    app.dependency_overrides = None
    response = client.get("/items/?q=foo&skip=100&limit=200")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "message": "Hello Items!",

# Exceptions - `HTTPException` and `WebSocketException`

These are the exceptions that you can raise to show errors to the client.

When you raise an exception, as would happen with normal Python, the rest of the execution is aborted. This way you can raise these exceptions from anywhere in the code to abort a request and show the error to the client.

You can use:

* `HTTPException`
* `WebSocketException`

Wenn Sie gleichzeitig eine Unteranwendung mounten (wie beschrieben in [Unteranwendungen – Mounts](sub-applications.md){.internal-link target=_blank}) und einen Proxy mit `root_path` verwenden wollen, können Sie das normal tun, wie Sie es erwarten würden.

    assert response.status_code == 200, response.text
    assert response.json() == {
        "message": "Hello Users!",
        "params": {"q": "foo", "skip": 5, "limit": 10},
    }


@needs_py310
def test_normal_app():
    from docs_src.dependency_testing.tutorial001_an_py310 import app, client

    app.dependency_overrides = None
    response = client.get("/items/?q=foo&skip=100&limit=200")

):
    return {
        "counter": count,
        "scope_counter_1": scope_count_1,
        "scope_counter_2": scope_count_2,
    }


client = TestClient(app)


def test_normal_counter():
    counter_holder["counter"] = 0
    response = client.get("/counter/")
    assert response.status_code == 200, response.text
    assert response.json() == {"counter": 1}
    response = client.get("/counter/")

It is just a standard function that can receive parameters.

It can be an `async def` or normal `def` function, **FastAPI** will know how to handle it correctly.

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

```Python hl_lines="6-9"
{!../../../docs_src/background_tasks/tutorial001.py!}
```