Bug: Tests using jest.useFakeTimers gave different results in react 17 and 18. about react

[42shadow42]

I think this is a feature: https://reactjs.org/blog/2022/03/29/react-v18.html#new-feature-automatic-batching

[skahack]

Thank you. I was able to get it to behave as before.
I don't know if this is the spec, but I'm going to close the Issue since it seems to have already been discussed.

https://codesandbox.io/p/sandbox/test-issue-repro-react18-resolved-5uxc9h

--- a.js        2023-03-02 13:52:47.000000000 +0900
+++ b.js        2023-03-02 13:52:59.000000000 +0900
@@ -1,27 +1,22 @@
 let TestRenderer
 let React
 let target
-let act
+
+global.IS_REACT_ACT_ENVIRONMENT = false
 
 beforeAll(() => {
   jest.useFakeTimers()
   TestRenderer = require('react-test-renderer')
   React = require('react')
   target = require('./hooks')
-  act = TestRenderer.act
 })
 
 it('', () => {
   const result = renderHook(target.useHooks)
 
-  act(() => {
-    jest.advanceTimersByTime(0)
-  })
+  jest.advanceTimersByTime(0)
   expect(target.count).toBe(0)
-
-  act(() => {
-    jest.advanceTimersByTime(500)
-  })
+  jest.advanceTimersByTime(501)
 
   expect(target.count).toBe(5)
   expect(result.current).toBe(6)