Test self-executing function wit Jest - unit-testing

Question

I understand reaching 100% unit test coverage shouldn't be a goal. I have actually excluded index.js from the coverage tests, I'm just interested to know how it would be done.
How can the self-executing function in index.js be tested? I'd like to test that it calls scrape.
index.js:
import scrape from './scrape';
const main = (async () => {
await scrape();
})();
export default main;
What I have tried:
import main from './index';
const scrape = jest.fn();
describe('On the index file', () => {
it('scrape executes automatically', async () => {
await main();
expect(scrape).toHaveBeenCalled();
});
});
This errors with TypeError: (0 , _index.default) is not a function
I see that main isn't a function but I haven't managed to make it work.

Answer 1

Here is my test strategy, you can use jest.mock(moduleName, factory, options) method mock the scrape module.
index.ts:
import scrape from './scrape';
const main = (async () => {
return await scrape();
})();
export default main;
index.spec.ts:
import scrape from './scrape';
import main from './';
jest.mock('./scrape.ts', () => jest.fn().mockResolvedValueOnce('fake data'));
describe('main', () => {
test('should return data', async () => {
const actualValue = await main;
expect(actualValue).toBe('fake data');
expect(scrape).toBeCalledTimes(1);
});
});
Unit test result with 100% coverage:
PASS src/stackoverflow/58674975/index.spec.ts (7.434s)
main
✓ should return data (5ms)
----------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files | 100 | 100 | 100 | 100 | |
index.ts | 100 | 100 | 100 | 100 | |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 8.684s
Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/58674975