Ember's settled() test helper, for React

settled

Stealing an idea from ember's settled test helper.

Assuming these conditions are true in your unit tests -

you're using Jest
and Jest's fake timers
and all your data requests are happening via fetch

You can call await settled() before making any assertions to make sure that -

all of React's updates are applied
all requests made have been resolved
all timers have run their course

(This has not been tested at all, buyer beware)

import { act } from "react-dom/test-utils";

let _fetchImpl = global.fetch;

let fetches = new Set();

global.fetch = async (...args) => {
  const promise = _fetchImpl(...args);
  fetches.add(promise);
  return promise.then(x => {
    fetches.delete(promise);
    return x;
  });
};

async function settled() {
  while (fetches.size > 0 && jest.getTimerCount() > 0) {
    await act(async () => {
      jest.runAllTimers();
      await Promise.all(fetches);
    });
  }
}

Usage

it('renders the page', async () => {
  render(<App/>);
  await settled();
  expect(queryByRole('button')).toExist(); // or your favourite assertions
});

threepointone/settled.react.md

settled

Usage