Trying to spyOn a mocked function - reactjs

Question

I am trying to perform a spyOn on a function that exists in a mocked class:
test.ts -
import Service from '../base_classes/Service';
jest.mock('../base_classes/Service');
const o: Component = new Component();
it('should load model specific information', async () => {
const getSpy = jest.spyOn(Service.prototype, 'get');
let t = await o.load(1);
expect(t.name).toEqual('test_name');
expect(getSpy).toHaveBeenCalledTimes(1);
});
__mocks__/Service.ts -
export const mockGet = jest.fn(async () => Promise.resolve({name:
'test_name'}));
const mock = jest.fn().mockImplementation(() => {
return {
get: mockGet
}
});
export default mock;
The resulting error is: Cannot spy the get property because it is not a function
I tried changing the mocked arrow function to a function(), but that didn't help.
How can I set this up so I can spy on my mocked function?

Answer 1

When using jest.mock it automatically creates a mock for each property of the module, replacing it's functions with jest.fn() (without implementation). And from then on you can write assertions. There should be no reason you'd want to spy on a mock function as it's already a mock function.
You should either spy on the actual implementation or write assertions for the methods on the mocked module.
e.g.
it('should load model specific information', async () => {
let t = await o.load(1);
expect(t.name).toEqual('test_name');
expect(Service.mock.instances[0].get).toHaveBeenCalledTimes(1);
});
working example