client = TestClient(app, cookies={"session": "fakesession"})
    with pytest.raises(WebSocketDisconnect):
        with client.websocket_connect("/items/foo/ws") as websocket:
            message = "Message one"
            websocket.send_text(message)
            data = websocket.receive_text()
            assert data == "Session cookie or query token value is: fakesession"
            data = websocket.receive_text()

## Documenting the callback

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

It could be just one or two lines of code, like:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

!!! check
    OpenAPI specifies that each *path operation* requires a response description.

    So, if you don't provide one, **FastAPI** will automatically generate one of "Successful response".

<img src="/img/tutorial/path-operation-configuration/image03.png">

## Deprecate a *path operation*

## Reduce duplication

Reducing code duplication is one of the core ideas in **FastAPI**.

As code duplication increments the chances of bugs, security issues, code desynchronization issues (when you update in one place but not in the others), etc.

And these models are all sharing a lot of the data and duplicating attribute names and types.

it will end up finishing some of the last tabs' requests earlier than some of the previous ones.

Then one the last requests that wait less seconds will try to open a database connection, but as one of those previous requests for the other tabs will probably be handled in the same thread as the first one, it will have the same database connection that is already open, and Peewee will throw an error and you will see it in the terminal, and the response will have an `Internal Server Error`....

        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="22"
    {!> ../../../docs_src/dependencies/tutorial005.py!}
    ```

!!! info
    Notice that we are only declaring one dependency in the *path operation function*, the `query_or_cookie_extractor`.

    But **FastAPI** will know that it has to solve `query_extractor` first, to pass the results of that to `query_or_cookie_extractor` while calling it.

    client = TestClient(app, cookies={"session": "fakesession"})
    with pytest.raises(WebSocketDisconnect):
        with client.websocket_connect("/items/foo/ws") as websocket:
            message = "Message one"
            websocket.send_text(message)
            data = websocket.receive_text()
            assert data == "Session cookie or query token value is: fakesession"
            data = websocket.receive_text()

    content: '';
    position: absolute;
    top: 15px;
    left: 15px;
    display: inline-block;
    width: 15px;
    height: 15px;
    border-radius: 50%;
    /* A little hack to display the window buttons in one pseudo element. */
    background: #d9515d;
    -webkit-box-shadow: 25px 0 0 #f4c025, 50px 0 0 #3ec930;
            box-shadow: 25px 0 0 #f4c025, 50px 0 0 #3ec930;
}

[data-termynal]:after {
    content: 'bash';

      description: |
        After submitting this, I commit to one of:

          * Read open questions until I find 2 where I can help someone and add a comment to help there.
          * I already hit the "watch" button in this repository to receive notifications and I commit to help at least 2 people that ask questions in the future.

---

But for this example, we'll use a very simple HTML document with some JavaScript, all inside a long string.

This, of course, is not optimal and you wouldn't use it for production.

In production you would have one of the options above.

But it's the simplest way to focus on the server-side of WebSockets and have a working example:

```Python hl_lines="2  6-38  41-43"
{!../../../docs_src/websockets/tutorial001.py!}
```