Wait.tests.js

describe('DiscoverQuery', () => {
  let called;
  let deferred;
  let oldFetch;

  beforeEach(() => {
    called = defer();
    deferred = defer();
    oldFetch = window.fetch;
    window.fetch = jest.fn().mockImplementation(async () => {
      const ret = await deferred.promise;
      setImmediate(called.resolve);
      return ret;
    });
  });

  afterEach(() => {
    cleanup();
    window.fetch = oldFetch;
  });

  it('renders DiscoverQuery', async()  => {
    const { getByTestId } = render(
          <DiscoverQuery>
            {results => <pre data-testid="json">{JSON.stringify(results, 0, 2)}</pre>}
          </DiscoverQuery>
    );

    deferred.resolve({
      ok: true,
      json: () => Promise.resolve(json),
    });

    await called.promise;

    expect(getByTestId('json')).toMatchSnapshot();
    
  });
});