## pytest.mark.anyio { #pytest-mark-anyio }

If we want to call asynchronous functions in our tests, our test functions have to be asynchronous. AnyIO provides a neat plugin for this, that allows us to specify that some test functions are to be called asynchronously.

## HTTPX { #httpx }

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

Como las dependencias también serán llamadas por **FastAPI** (lo mismo que tus *path operation functions*), las mismas reglas aplican al definir tus funciones.

Puedes usar `async def` o `def` normal.

Y puedes declarar dependencias con `async def` dentro de *path operation functions* normales `def`, o dependencias `def` dentro de *path operation functions* `async def`, etc.

No importa. **FastAPI** sabrá qué hacer.

/// note | Nota

///

/// tip

If you want to call `async` functions in your tests apart from sending requests to your FastAPI application (e.g. asynchronous database functions), have a look at the [Async Tests](../advanced/async-tests.md){.internal-link target=_blank} in the advanced tutorial.

///

## Separating tests { #separating-tests }

### Otras funciones de utilidad { #other-utility-functions }

Cualquier otra función de utilidad que llames directamente puede ser creada con `def` normal o `async def` y FastAPI no afectará la forma en que la llames.

Esto contrasta con las funciones que FastAPI llama por ti: *path operation functions* y dependencias.

    return {"fresh_value": fresh_value}
```

////

## Recap { #recap }

Apart from all the fancy words used here, the **Dependency Injection** system is quite simple.

Just functions that look the same as the *path operation functions*.

But still, it is very powerful, and allows you to declare arbitrarily deeply nested dependency "graphs" (trees).

/// tip

All this might not seem as useful with these simple examples.

Maybe you need to start a new version, or you just got tired of running it. 🤷

///

### Lifespan function { #lifespan-function }

The first thing to notice, is that we are defining an async function with `yield`. This is very similar to Dependencies with `yield`.

{* ../../docs_src/events/tutorial003_py39.py hl[14:19] *}

The first part of the function, before the `yield`, will be executed **before** the application starts.

But then we get a `dict` in the parameter `commons` of the *path operation function*.

And we know that editors can't provide a lot of support (like completion) for `dict`s, because they can't know their keys and value types.

We can do better...

## What makes a dependency { #what-makes-a-dependency }

Up to now you have seen dependencies declared as functions.

/// note | Technical Details

When you import `Query`, `Path` and others from `fastapi`, they are actually functions.

That when called, return instances of classes of the same name.

So, you import `Query`, which is a function. And when you call it, it returns an instance of a class also named `Query`.

These functions are there (instead of just using the classes directly) so that your editor doesn't mark errors about their types.

Then, the arguments of the call are <i>passed</i> to the function,
which means that they are <a href="#Assignment_statements">assigned</a>
to their corresponding function parameters,
and the called function begins execution.
The return parameters of the function are passed
back to the caller when the function returns.
</p>

<p>
Calling a <code>nil</code> function value
causes a <a href="#Run_time_panics">run-time panic</a>.

{* ../../docs_src/custom_docs_ui/tutorial001_py39.py hl[8] *}

### Include the custom docs { #include-the-custom-docs }

Now you can create the *path operations* for the custom docs.

You can reuse FastAPI's internal functions to create the HTML pages for the docs, and pass them the needed arguments:

* `openapi_url`: the URL where the HTML page for the docs can get the OpenAPI schema for your API. You can use here the attribute `app.openapi_url`.