import pytest
from rest_framework import status

@pytest.mark.django_db
def test_invoice_access_restriction(api_client, regular_user, invoice_a):
    # invoice_a pripada serviseru_a, a api_client je regular_user
    url = f'/api/invoicing/invoices/{invoice_a.id}/'
    response = api_client.get(url)
    # Trebao bi dobiti 404 ili 403 ovisno o tvojoj logici
    assert response.status_code in [status.HTTP_404_NOT_FOUND, status.HTTP_403_FORBIDDEN]