test(unmount): Add expected behavior for unmount() and cleanup functions

src/__tests__/render.js

@@ -1,6 +1,8 @@
 import React from 'react'
 import ReactDOM from 'react-dom'
 import {render, screen} from '../'
+import {cleanup} from '../pure'
+import {act} from 'react-dom/test-utils'
 
 test('renders div into document', () => {
   const ref = React.createRef()
@@ -87,3 +89,17 @@ test('renders options.wrapper around node', () => {
 </div>
 `)
 })
+
+test('flushes useEffect cleanup functions sync on unmount()', () => {
+  const spy = jest.fn()
+  function Component() {
+    React.useEffect(() => spy, [])
+    return null
+  }
+  const {unmount} = render(<Component />)
+  expect(spy).toHaveBeenCalledTimes(0)
+
+  unmount()
+
+  expect(spy).toHaveBeenCalledTimes(1)
+})