Unit testing in nodejs with jest

I want to unit test my functions, but I have stopped when creating a mock to simulate the creation of a resource, I am using mongoose in a feathers project (nodejs). To do the unit tests I use the jest plugin. Here the function I want to test.

 export async function saveCar(a: string, b: string) {
  const carModel = mongoose.model('car');
  const car = new carModel({ a, b});
  await car.save();

To simulate the search by id I have used this mock:

jest.mock('mongoose', () => ({
  model () {
    return {
      findById () {
        return Promise.resolve(undefined);

The function I use for this is:

export async function getCar (id: string) {
  const carModel = mongoose.model('car');
  return await carModel.findById(id);