I'm trying to write a unit test for my API using Jest and I'm using some boilerplate code but it's leading me to an error that I don't understand. Here is the test:

describe('findAll', () => {
it('should return an array of cats', async () => {
  const result = ['test'];
  jest.spyOn(catsService, 'findAll').mockImplementation(() => result);

  expect(await catsController.findAll()).toBe(result);
  });
});

The error is in the part () => result:

Type 'string[]' is not assignable to type 'Cat[]'

My findAll method within catsController is very straightforward, it just return an array of Cat objects:

findAll(): Cat[] {
return this.catsService.findAll();
}

What is incorrect about my mockImplementation?