act.js

let called = false;
// this 'scope' is safe to interact with the React component,
// rendering and clicking as you please
await render(
  <App
    callback={() => {
      called = true;
    }}
  />,
  document.body
);
// at this point, we can guarantee that effects have been executed,
// so we can make assertions
expect(called).toBe(true); // this passes now!

const button = document.getElementById('button');
await dispatchEvent(button, new MouseEvent('click', {bubbles: true}))