## Separating tests

In a real application, you probably would have your tests in a different file.

And your **FastAPI** application might also be composed of several files/modules, etc.

### **FastAPI** app file

Let's say you have a file structure as described in [Bigger Applications](bigger-applications.md){.internal-link target=_blank}:

```
.

# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/tiangolo/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment with `venv`

But first, let's check some small concepts.

## In a hurry?

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

## OAuth2

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

## About "Form Fields"

The way HTML forms (`<form></form>`) sends the data to the server normally uses a "special" encoding for that data, it's different from JSON.

**FastAPI** will make sure to read that data from the right place instead of JSON.

!!! note "Technical Details"
    Data from forms is normally encoded using the "media type" `application/x-www-form-urlencoded`.

This includes, for example:

* Email notifications sent after performing an action:
    * As connecting to an email server and sending an email tends to be "slow" (several seconds), you can return the response right away and send the email notification in the background.
* Processing data:

```Python hl_lines="9-11"
{!../../../docs_src/sql_databases_peewee/sql_app/main.py!}
```

### Create a dependency

Create a dependency that will connect the database right at the beginning of a request and disconnect it at the end:

```Python hl_lines="23-29"
{!../../../docs_src/sql_databases_peewee/sql_app/main.py!}
```

## Do not Separate Schemas

Now, there are some cases where you might want to have the **same schema for input and output**.

Probably the main use case for this is if you already have some autogenerated client code/SDKs and you don't want to update all the autogenerated client code/SDKs yet, you probably will want to do it at some point, but maybe not right now.

The **Advanced User Guide**, builds on this, uses the same concepts, and teaches you some extra features.

But you should first read the **Tutorial - User Guide** (what you are reading right now).

## What is "Form Data"

The way HTML forms (`<form></form>`) sends the data to the server normally uses a "special" encoding for that data, it's different from JSON.

**FastAPI** will make sure to read that data from the right place instead of JSON.

!!! note "Technical Details"
    Data from forms is normally encoded using the "media type" `application/x-www-form-urlencoded` when it doesn't include files.

The benefit of raising an exception over `return`ing a value will be more evident in the section about Dependencies and Security.