While you are at the line, you are just idle 😴, waiting for your turn, not doing anything very "productive". But the line is fast because the cashier is only taking the orders (not preparing them), so that's fine.

Then, when it's your turn, you do actual "productive" work, you process the menu, decide what you want, get your crush's choice, pay, check that you give the correct bill or card, check that you are charged correctly, check that the order has the correct items, etc.

This gives you a lot of flexibility. You can return any data type, override any data declaration or validation, etc.

## Using the `jsonable_encoder` in a `Response`

Because **FastAPI** doesn't make any changes to a `Response` you return, you have to make sure its contents are ready for it.

You also define in some way at which **moments** your app will send those requests or events.

And **your users** define in some way (for example in a web dashboard somewhere) the **URL** where your app should send those requests.

### Use cases: external service

An example could be that you have an external authentication provider that you need to call.

You send it a token and it returns an authenticated user.

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

You probably want to test the external provider once, but not necessarily call it for every test that runs.

But it's possible to customize it, you can set a specific CDN, or serve the files yourself.

## Custom CDN for JavaScript and CSS

Let's say that you want to use a different <abbr title="Content Delivery Network">CDN</abbr>, for example you want to use `https://unpkg.com/`.

This could be useful if for example you live in a country that restricts some URLs.

### Disable the automatic docs

/// warning

This is a rather advanced topic.

If you are starting with **FastAPI**, you might not need this.

///

You can declare additional responses, with additional status codes, media types, descriptions, etc.

Those additional responses will be included in the OpenAPI schema, so they will also appear in the API docs.

If you have a Pydantic model in your test and you want to send its data to the application during testing, you can use the `jsonable_encoder` described in [JSON Compatible Encoder](encoder.md){.internal-link target=_blank}.

///

## Run it

After that, you just need to install `pytest`.

If you don't select any scope, you will be "authenticated", but when you try to access `/users/me/` or `/users/me/items/` you will get an error saying that you don't have enough permissions. You will still be able to access `/status/`.

And if you select the scope `me` but not the scope `items`, you will be able to access `/users/me/` but not `/users/me/items/`.

And the next sections assume you already read it, and assume that you know those main ideas.

## External Courses

Although the [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank} and this **Advanced User Guide** are written as a guided tutorial (like a book) and should be enough for you to **learn FastAPI**, you might want to complement it with additional courses.

## Bodies of arbitrary `dict`s

You can also declare a body as a `dict` with keys of some type and values of some other type.

This way, you don't have to know beforehand what the valid field/attribute names are (as would be the case with Pydantic models).

This would be useful if you want to receive keys that you don't already know.

---

Another useful case is when you want to have keys of another type (e.g., `int`).