For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

## Use cases { #use-cases }

Some use cases include:

from fastapi.testclient import TestClient

from docs_src.cors.tutorial001_py39 import app


def test_cors():
    client = TestClient(app)
    # Test pre-flight response
    headers = {
        "Origin": "https://localhost.tiangolo.com",
        "Access-Control-Request-Method": "GET",
        "Access-Control-Request-Headers": "X-Example",
    }
    response = client.options("/", headers=headers)

import os
from pathlib import Path

import pytest
from fastapi.testclient import TestClient


@pytest.fixture(scope="module")
def client():
    static_dir: Path = Path(os.getcwd()) / "static"
    print(static_dir)
    static_dir.mkdir(exist_ok=True)
    from docs_src.custom_docs_ui.tutorial002_py39 import app

    with TestClient(app) as client:
        yield client
    static_dir.rmdir()

import importlib

import pytest
from fastapi.testclient import TestClient
from pytest import MonkeyPatch


@pytest.fixture(name="app", params=[pytest.param("tutorial001_py39")])
def get_app(request: pytest.FixtureRequest, monkeypatch: MonkeyPatch):
    monkeypatch.setenv("ADMIN_EMAIL", "******@****.***")
    mod = importlib.import_module(f"docs_src.settings.{request.param}")
    return mod.app


def test_settings(app):

from fastapi.testclient import TestClient

from docs_src.metadata.tutorial001_py39 import app

client = TestClient(app)


def test_items():
    response = client.get("/items/")
    assert response.status_code == 200, response.text
    assert response.json() == [{"name": "Katana"}]


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {

import importlib

import pytest
from fastapi.testclient import TestClient

from ...utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        "tutorial001_py39",
        pytest.param("tutorial001_py310", marks=needs_py310),
    ],
)
def get_client(request: pytest.FixtureRequest):
    mod = importlib.import_module(f"docs_src.body_updates.{request.param}")

    client = TestClient(mod.app)

import importlib

import pytest
from fastapi.testclient import TestClient
from inline_snapshot import snapshot

from tests.utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        "tutorial001_py39",
        pytest.param("tutorial001_py310", marks=needs_py310),
        "tutorial001_an_py39",
        pytest.param("tutorial001_an_py310", marks=needs_py310),
    ],
)

from typing import Union

import pytest
from fastapi import FastAPI
from fastapi.exceptions import FastAPIError, ResponseValidationError
from fastapi.responses import JSONResponse, Response
from fastapi.testclient import TestClient
from pydantic import BaseModel


class BaseUser(BaseModel):
    name: str


class User(BaseUser):
    surname: str


class DBUser(User):
    password_hash: str


class Item(BaseModel):

Wenn etwas für Ihr Projekt interessant und nützlich erscheint, lesen Sie es, andernfalls überspringen Sie es einfach.

/// tip | Tipp

Wenn Sie strukturiert **FastAPI lernen** möchten (empfohlen), lesen Sie stattdessen Kapitel für Kapitel das [Tutorial – Benutzerhandbuch](../tutorial/index.md){.internal-link target=_blank}.

Similar a como puedes [agregar `dependencies` a los *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, puedes agregarlos a la aplicación de `FastAPI`.

En ese caso, se aplicarán a todas las *path operations* en la aplicación:

{* ../../docs_src/dependencies/tutorial012_an_py39.py hl[17] *}