from typing_extensions import Annotated

app = FastAPI()


class FormModel(BaseModel):
    username: str
    lastname: str
    age: Optional[int] = None
    tags: List[str] = ["foo", "bar"]
    alias_with: str = Field(alias="with", default="nothing")


@app.post("/form/")
def post_form(user: Annotated[FormModel, Form()]):
    return user


client = TestClient(app)