Refer to: https://github.com/vuejs/core/actions/runs/3458391480/jobs/5772768354

In test:

patchProp(child, 'onClick', null, () => {
  childFn()
  patchProp(el, 'onClick', null, parentFn)
})
child.dispatchEvent(new Event('click', { bubbles: true }))

The above code (including the event handler) is executed in the same loop in nodejs.

Because use the same timestamp for all event listeners attached in the same tick in createInvoker.
The attached timestamp of parentFn event will be earlier than the bubble event.
So the parentFn will have been called.

To avoid unstable tests, move dispatchEvent to next loop.