feat: use act to flush instead of custom implementation (#768)

BREAKING CHANGE: cleanup is now synchronous and wraps the unmounting process in `act`.

Author: eps1lon

Diff for: src/__tests__/cleanup.js

@@ -1,7 +1,7 @@
 import React from 'react'
 import {render, cleanup} from '../'
 
-test('cleans up the document', async () => {
+test('cleans up the document', () => {
   const spy = jest.fn()
   const divId = 'my-div'
 
@@ -17,17 +17,17 @@ test('cleans up the document', async () => {
   }
 
   render(<Test />)
-  await cleanup()
+  cleanup()
   expect(document.body).toBeEmptyDOMElement()
   expect(spy).toHaveBeenCalledTimes(1)
 })
 
-test('cleanup does not error when an element is not a child', async () => {
+test('cleanup does not error when an element is not a child', () => {
   render(<div />, {container: document.createElement('div')})
-  await cleanup()
+  cleanup()
 })
 
-test('cleanup runs effect cleanup functions', async () => {
+test('cleanup runs effect cleanup functions', () => {
   const spy = jest.fn()
 
   const Test = () => {
@@ -37,6 +37,87 @@ test('cleanup runs effect cleanup functions', async () => {
   }
 
   render(<Test />)
-  await cleanup()
+  cleanup()
   expect(spy).toHaveBeenCalledTimes(1)
 })
+
+describe('fake timers and missing act warnings', () => {
+  beforeEach(() => {
+    jest.resetAllMocks()
+    jest.spyOn(console, 'error').mockImplementation(() => {
+      // assert messages explicitly
+    })
+    jest.useFakeTimers()
+  })
+
+  afterEach(() => {
+    jest.useRealTimers()
+  })
+
+  test('cleanup does not flush immediates', () => {
+    const microTaskSpy = jest.fn()
+    function Test() {
+      const counter = 1
+      const [, setDeferredCounter] = React.useState(null)
+      React.useEffect(() => {
+        let cancelled = false
+        setImmediate(() => {
+          microTaskSpy()
+          if (!cancelled) {
+            setDeferredCounter(counter)
+          }
+        })
+
+        return () => {
+          cancelled = true
+        }
+      }, [counter])
+
+      return null
+    }
+    render(<Test />)
+
+    cleanup()
+
+    expect(microTaskSpy).toHaveBeenCalledTimes(0)
+    // console.error is mocked
+    // eslint-disable-next-line no-console
+    expect(console.error).toHaveBeenCalledTimes(0)
+  })
+
+  test('cleanup does not swallow missing act warnings', () => {
+    const deferredStateUpdateSpy = jest.fn()
+    function Test() {
+      const counter = 1
+      const [, setDeferredCounter] = React.useState(null)
+      React.useEffect(() => {
+        let cancelled = false
+        setImmediate(() => {
+          deferredStateUpdateSpy()
+          if (!cancelled) {
+            setDeferredCounter(counter)
+          }
+        })
+
+        return () => {
+          cancelled = true
+        }
+      }, [counter])
+
+      return null
+    }
+    render(<Test />)
+
+    jest.runAllImmediates()
+    cleanup()
+
+    expect(deferredStateUpdateSpy).toHaveBeenCalledTimes(1)
+    // console.error is mocked
+    // eslint-disable-next-line no-console
+    expect(console.error).toHaveBeenCalledTimes(1)
+    // eslint-disable-next-line no-console
+    expect(console.error.mock.calls[0][0]).toMatch(
+      'a test was not wrapped in act(...)',
+    )
+  })
+})

Diff for: src/flush-microtasks.js

@@ -7,7 +7,6 @@ import {
 } from '@testing-library/dom'
 import act, {asyncAct} from './act-compat'
 import {fireEvent} from './fire-event'
-import flush from './flush-microtasks'
 
 configureDTL({
   asyncWrapper: async cb => {
@@ -100,17 +99,16 @@ function render(
   }
 }
 
-async function cleanup() {
+function cleanup() {
   mountedContainers.forEach(cleanupAtContainer)
-  // flush microtask queue after unmounting in case
-  // unmount sequence generates new microtasks
-  await flush()
 }
 
 // maybe one day we'll expose this (perhaps even as a utility returned by render).
 // but let's wait until someone asks for it.
 function cleanupAtContainer(container) {
-  ReactDOM.unmountComponentAtNode(container)
+  act(() => {
+    ReactDOM.unmountComponentAtNode(container)
+  })
   if (container.parentNode === document.body) {
     document.body.removeChild(container)
   }