if lang_path.is_dir() and lang_path.name.startswith(incomplete):
            yield lang_path.name


@app.callback()
def callback() -> None:
    # For MacOS with Cairo
    os.environ["DYLD_FALLBACK_LIBRARY_PATH"] = "/opt/homebrew/lib"


@app.command()
def new_lang(lang: str = typer.Argument(..., callback=lang_callback)):
    """

router_a.include_router(
    router_a_b_override, prefix="/b", default_response_class=PlainTextResponse
)
app.include_router(router_a, prefix="/a")
app.include_router(
    router_b_override, prefix="/b", default_response_class=PlainTextResponse
)


client = TestClient(app)

json_type = "application/json"
text_type = "text/plain; charset=utf-8"
html_type = "text/html; charset=utf-8"

///

### Pydantic v1 and v2 on the same app { #pydantic-v1-and-v2-on-the-same-app }

It's **not supported** by Pydantic to have a model of Pydantic v2 with its own fields defined as Pydantic v1 models or vice versa.

```mermaid
graph TB
    subgraph "❌ Not Supported"

             the following code:

             <u style="text-decoration-style:solid">from </u><u style="text-decoration-style:solid"><b>main</b></u><u style="text-decoration-style:solid"> import </u><u style="text-decoration-style:solid"><b>app</b></u>

      prefixes = ["/api/v1"]

  [http.routers]

    [http.routers.app-http]
      entryPoints = ["http"]
      service = "app"
      rule = "PathPrefix(`/api/v1`)"
      middlewares = ["api-stripprefix"]

  [http.services]

    [http.services.app]
      [http.services.app.loadBalancer]
        [[http.services.app.loadBalancer.servers]]
          url = "http://127.0.0.1:8000"
```

from typing import Optional

from fastapi import FastAPI
from fastapi.params import Param
from fastapi.testclient import TestClient

app = FastAPI()


@app.get("/items/")
def read_items(q: Optional[str] = Param(default=None)):  # type: ignore
    return {"q": q}


client = TestClient(app)


def test_default_param_query_none():
    response = client.get("/items/")
    assert response.status_code == 200, response.text

            return dt_field.replace(microsecond=0, tzinfo=timezone.utc).isoformat()

    app = FastAPI()
    model = ModelWithDatetimeField(dt_field=datetime(2019, 1, 1, 8))

    @app.get("/model", response_model=ModelWithDatetimeField)
    def get_model():
        return model

    client = TestClient(app)
    with client:
        response = client.get("/model")

from typing import Optional

from fastapi import FastAPI, Security
from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
from fastapi.testclient import TestClient

app = FastAPI()

security = HTTPBearer(auto_error=False)


@app.get("/users/me")
def read_current_user(
    credentials: Optional[HTTPAuthorizationCredentials] = Security(security),
):
    if credentials is None:

from fastapi.testclient import TestClient

app = FastAPI()

oauth2_scheme = OAuth2AuthorizationCodeBearer(
    authorizationUrl="authorize",
    tokenUrl="token",
    description="OAuth2 Code Bearer",
    auto_error=True,
)


@app.get("/items/")
async def read_items(token: Optional[str] = Security(oauth2_scheme)):
    return {"token": token}


client = TestClient(app)


def test_no_token():

from fastapi.testclient import TestClient

app = FastAPI()

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


@app.get("/items/")
async def read_items(token: Optional[str] = Security(oauth2_scheme)):
    if token is None:
        return {"msg": "Create an account first"}
    return {"token": token}


client = TestClient(app)


def test_no_token():