App.out-of-scope.test.js

import React from 'react';
import { render } from '@testing-library/react';
import App from './App';

jest.mock('./MyComponent', () => () => {
  React.useEffect(() => {
    console.log('using an effect');
  });
  return (<div>Hello World</div>);
});

test('renders', () => {
  const { container } = render(<App/>);
  expect(container.textContent)
    .toMatch('Hello World');
});