if both include and router path are empty it should raise exception if both include and router path are empty it should raise exception
import pytest
from fastapi import APIRouter, FastAPI
from fastapi.exceptions import FastAPIError
from fastapi.testclient import TestClient

app = FastAPI()

router = APIRouter()


@router.get("")
def get_empty():
    return ["OK"]


app.include_router(router, prefix="/prefix")


client = TestClient(app)


def test_use_empty():
    with client:
        response = client.get("/prefix")
        assert response.status_code == 200, response.text
        assert response.json() == ["OK"]

        response = client.get("/prefix/")
        assert response.status_code == 200, response.text
        assert response.json() == ["OK"]


def test_include_empty():
    
    with pytest.raises(FastAPIError):
        app.include_router(router)