from pydantic import BaseModel, ConfigDict, Field


@pytest.fixture(name="client")
def get_client():
    app = FastAPI()

    class ModelWithRef(BaseModel):
        ref: str = Field(validation_alias="$ref", serialization_alias="$ref")
        model_config = ConfigDict(validate_by_alias=True, serialize_by_alias=True)

    @app.get("/", response_model=ModelWithRef)
    async def read_root() -> Any:
        return {"$ref": "some-ref"}

        va = self.field_info.validation_alias
        if isinstance(va, str) and va:
            return va
        return None

    @property
    def serialization_alias(self) -> str | None:
        sa = self.field_info.serialization_alias
        return sa or None

    @property
    def default(self) -> Any:
        return self.get_default()

    def __post_init__(self) -> None:

    * `Cookie()`
    * `Body()`
    * `Form()`
    * `File()`

* The new parameter fields are:

    * `default_factory`
    * `alias_priority`
    * `validation_alias`
    * `serialization_alias`
    * `discriminator`
    * `strict`
    * `multiple_of`
    * `allow_inf_nan`
    * `max_digits`
    * `decimal_places`
    * `json_schema_extra`