auth.js

export default {
  isAllowed() {
    return false;
  }
};

model.js

import auth from './auth'

export default {
  findCar() {
    if (auth.isAllowed()) return "A car";
  }
};

tests.js

import Car from './model';

const auth = {
  isAllowed() { return true; },
};

Car.findCar(auth);