Sometimes it can be useful to await until all currently queued Promises and microtasks have been processed.

(Note: this flushes the microtask queue by scheduling a new macrotask with setTimeout, allowing any pending Promise callbacks to execute before continuing)

import { act } from '@testing-library/react';

// wrapped in React's act(). If you aren't
// testing React you can remove the act part!
const flushPromises = async () => {
  await act(async () => new Promise(resolve => setTimeout(resolve, 0)));
};

Use it like this:

// component automatically fetches data on initial render
render(<SomeComponent />);

await flushPromises();

expect(window.fetch).toHaveBeenCalledTimes(1);