return [{"item_id": "i1", "user_id": "u1"}, {"item_id": "i2", "user_id": "u2"}]
    else:
        return [{"item_id": "i2", "user_id": user_id}]


@item_router.get("/{item_id}")
def get_item(item_id: str, user_id: Optional[str] = None):
    if user_id is None:
        return {"item_id": item_id}
    else:
        return {"item_id": item_id, "user_id": user_id}

As the testing function is now asynchronous, you can now also call (and `await`) other `async` functions apart from sending requests to your FastAPI application in your tests, exactly as you would call them anywhere else in your code.

!!! tip

<img src="/img/tutorial/custom-response/image01.png">

## Available responses

Here are some of the available responses.

Keep in mind that you can use `Response` to return anything else, or even create a custom sub-class.

!!! note "Technical Details"
    You could also use `from starlette.responses import HTMLResponse`.

By validating the data with Pydantic we can make sure that we have, for example, exactly a `list` of `str` with the scopes and a `str` with the `username`.

Instead of, for example, a `dict`, or something else, as it could break the application at some point later, making it a security risk.

We also verify that we have a user with that username, and if not, we raise that same exception we created before.

=== "Python 3.10+"

        )
        self.exception_handlers: Dict[
            Any, Callable[[Request, Any], Union[Response, Awaitable[Response]]]
        ] = {} if exception_handlers is None else dict(exception_handlers)
        self.exception_handlers.setdefault(HTTPException, http_exception_handler)
        self.exception_handlers.setdefault(
            RequestValidationError, request_validation_exception_handler

        dependant.request_param_name = param_name
        return True
    elif lenient_issubclass(type_annotation, WebSocket):
        dependant.websocket_param_name = param_name
        return True
    elif lenient_issubclass(type_annotation, HTTPConnection):
        dependant.http_connection_param_name = param_name
        return True
    elif lenient_issubclass(type_annotation, Response):

        if field_info.description:
            parameter["description"] = field_info.description
        if field_info.openapi_examples:
            parameter["examples"] = jsonable_encoder(field_info.openapi_examples)
        elif field_info.example != Undefined:
            parameter["example"] = jsonable_encoder(field_info.example)
        if field_info.deprecated:
            parameter["deprecated"] = True
        parameters.append(parameter)

    if not file:
        return {"message": "No file sent"}
    else:
        return {"file_size": len(file)}


@app.post("/uploadfile/")
async def create_upload_file(file: Union[UploadFile, None] = None):
    if not file:
        return {"message": "No upload file sent"}
    else:

class RoleEnum(Enum):
    admin = "admin"
    normal = "normal"


class ModelWithConfig(BaseModel):
    role: Optional[RoleEnum] = None

    if PYDANTIC_V2:
        model_config = {"use_enum_values": True}
    else:

        class Config:
            use_enum_values = True


class ModelWithAlias(BaseModel):
    foo: str = Field(alias="Foo")


class ModelWithDefault(BaseModel):
    foo: str = ...  # type: ignore

        if not api_key:
            if self.auto_error:
                raise HTTPException(
                    status_code=HTTP_403_FORBIDDEN, detail="Not authenticated"
                )
            else:
                return None
        return api_key


class APIKeyHeader(APIKeyBase):
    """
    API key authentication using a header.