You can use the `TestClient` class to test FastAPI applications without creating an actual HTTP and socket connection, just communicating directly with the FastAPI code.

Read more about it in the [FastAPI docs for Testing](https://fastapi.tiangolo.com/tutorial/testing/).

You can import it directly from `fastapi.testclient`:

```python
from fastapi.testclient import TestClient
```

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[str | None, Query(title="Query string", min_length=3)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Annotated

from fastapi import Cookie, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Cookies(BaseModel):
    session_id: str
    fatebook_tracker: str | None = None
    googall_tracker: str | None = None


@app.get("/items/")
async def read_items(cookies: Annotated[Cookies, Cookie()]):

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/", tags=["items"])
async def read_items():
    return [{"name": "Foo", "price": 42}]


@app.get("/users/", tags=["users"])
async def read_users():
    return [{"username": "johndoe"}]


@app.get("/elements/", tags=["items"], deprecated=True)
async def read_elements():

from typing import Annotated

from fastapi import FastAPI, Path

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(
    item_id: Annotated[int, Path(title="The ID of the item to get", ge=1)], q: str
):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

from fastapi import FastAPI, Response, status

app = FastAPI()

tasks = {"foo": "Listen to the Bar Fighters"}


@app.put("/get-or-create-task/{task_id}", status_code=200)
def get_or_create_task(task_id: str, response: Response):
    if task_id not in tasks:
        tasks[task_id] = "This didn't exist before"
        response.status_code = status.HTTP_201_CREATED

from fastapi import FastAPI, Security
from fastapi.security import OAuth2PasswordBearer
from fastapi.testclient import TestClient
from inline_snapshot import snapshot

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(
    tokenUrl="/token",
    description="OAuth2PasswordBearer security scheme",
    auto_error=False,
)


@app.get("/items/")
async def read_items(token: str | None = Security(oauth2_scheme)):
    if token is None:

**FastAPI**は、この依存関係を使用してOpenAPIスキーマ (および自動APIドキュメント) で「セキュリティスキーム」を定義できることを知っています。

/// info | 技術詳細

**FastAPI**は、`OAuth2PasswordBearer` クラス (依存関係で宣言されている) を使用してOpenAPIのセキュリティスキームを定義できることを知っています。これは`fastapi.security.oauth2.OAuth2`、`fastapi.security.base.SecurityBase`を継承しているからです。

OpenAPIと統合するセキュリティユーティリティ (および自動APIドキュメント) はすべて`SecurityBase`を継承しています。それにより、**FastAPI**はそれらをOpenAPIに統合する方法を知ることができます。

///

import json
from typing import Annotated, Any

import pytest
from fastapi import APIRouter, Depends, FastAPI, HTTPException
from fastapi.exceptions import FastAPIError
from fastapi.responses import StreamingResponse
from fastapi.testclient import TestClient


class Session:
    def __init__(self) -> None:
        self.open = True


def dep_session() -> Any:
    s = Session()
    yield s
    s.open = False

from fastapi import Depends, FastAPI, Security
from fastapi.security.open_id_connect_url import OpenIdConnect
from fastapi.testclient import TestClient
from inline_snapshot import snapshot
from pydantic import BaseModel

app = FastAPI()

oid = OpenIdConnect(openIdConnectUrl="/openid")


class User(BaseModel):
    username: str


def get_current_user(oauth_header: str = Security(oid)):
    user = User(username=oauth_header)