Do we need to use react-dom/test-utils act() function?

README.md

@@ -2,10 +2,16 @@
 <h1>react-testing-library</h1>
 
 <a href="https://www.emojione.com/emoji/1f410">
-<img height="80" width="80" alt="goat" src="https://raw.githubusercontent.com/kentcdodds/react-testing-library/master/other/goat.png" />
+  <img
+    height="80"
+    width="80"
+    alt="goat"
+    src="https://raw.githubusercontent.com/kentcdodds/react-testing-library/master/other/goat.png"
+  />
 </a>
 
-<p>Simple and complete React DOM testing utilities that encourage good testing practices.</p>
+<p>Simple and complete React DOM testing utilities that encourage good testing
+practices.</p>
 
 [**Read The Docs**](https://testing-library.com/react) |
 [Edit the docs](https://github.com/alexkrolick/testing-library-docs)
@@ -30,9 +36,13 @@
 <!-- prettier-ignore-end -->
 
 <div align="center">
-<a href="https://testingjavascript.com">
-<img width="500" alt="TestingJavaScript.com Learn the smart, efficient way to test any JavaScript application." src="https://raw.githubusercontent.com/kentcdodds/react-testing-library/master/other/testingjavascript.jpg" />
-</a>
+  <a href="https://testingjavascript.com">
+    <img
+      width="500"
+      alt="TestingJavaScript.com Learn the smart, efficient way to test any JavaScript application."
+      src="https://raw.githubusercontent.com/kentcdodds/react-testing-library/master/other/testingjavascript.jpg"
+    />
+  </a>
 </div>
 
 ## Table of Contents
@@ -102,7 +112,7 @@ test('Fetch makes an API call and displays the greeting when load-greeting is cl
   )
 
   // Act
-  fireEvent.click(getByText('Load Greeting'))
+  fireEvent.click(getByText(/load greeting/i))
 
   // Let's wait until our mocked `get` request promise resolves and
   // the component calls setState and re-renders.

package.json

@@ -48,8 +48,8 @@
     "jest-dom": "^2.0.4",
     "jest-in-case": "^1.0.2",
     "kcd-scripts": "^0.44.0",
-    "react": "16.8.0",
-    "react-dom": "16.8.0",
+    "react": "^16.8.0",
+    "react-dom": "^16.8.0",
     "react-redux": "^5.0.7",
     "react-router": "^4.3.1",
     "react-router-dom": "^4.3.1",

src/__tests__/act.js

@@ -0,0 +1,42 @@
+import 'jest-dom/extend-expect'
+import React from 'react'
+import {render, cleanup, fireEvent} from '../'
+
+afterEach(cleanup)
+
+test('render calls useEffect immediately', () => {
+  const effectCb = jest.fn()
+  function MyUselessComponent() {
+    React.useEffect(effectCb)
+    return null
+  }
+  render(<MyUselessComponent />)
+  expect(effectCb).toHaveBeenCalledTimes(1)
+})
+
+test('fireEvent triggers useEffect calls', () => {
+  const effectCb = jest.fn()
+  function Counter() {
+    React.useEffect(effectCb)
+    const [count, setCount] = React.useState(0)
+    return <button onClick={() => setCount(count + 1)}>{count}</button>
+  }
+  const {
+    container: {firstChild: buttonNode},
+  } = render(<Counter />)
+
+  effectCb.mockClear()
+  fireEvent.click(buttonNode)
+  expect(buttonNode).toHaveTextContent('1')
+  expect(effectCb).toHaveBeenCalledTimes(1)
+})
+
+test('calls to hydrate will run useEffects', () => {
+  const effectCb = jest.fn()
+  function MyUselessComponent() {
+    React.useEffect(effectCb)
+    return null
+  }
+  render(<MyUselessComponent />, {hydrate: true})
+  expect(effectCb).toHaveBeenCalledTimes(1)
+})

src/__tests__/no-act.js

@@ -0,0 +1,10 @@
+import {act} from '..'
+
+jest.mock('react-dom/test-utils', () => ({}))
+
+test('act works even when there is no act from test utils', () => {
+  const callback = jest.fn()
+  act(callback)
+  expect(callback).toHaveBeenCalledTimes(1)
+  expect(callback).toHaveBeenCalledWith(/* nothing */)
+})

src/__tests__/render.js

@@ -1,7 +1,7 @@
 import 'jest-dom/extend-expect'
 import React from 'react'
 import ReactDOM from 'react-dom'
-import {render, cleanup, flushEffects} from '../'
+import {render, cleanup} from '../'
 
 afterEach(cleanup)
 
@@ -90,10 +90,3 @@ it('supports fragments', () => {
   cleanup()
   expect(document.body.innerHTML).toBe('')
 })
-
-test('flushEffects can be called without causing issues', () => {
-  render(<div />)
-  const preHtml = document.documentElement.innerHTML
-  flushEffects()
-  expect(document.documentElement.innerHTML).toBe(preHtml)
-})

src/act-compat.js

@@ -0,0 +1,12 @@
+import {act as reactAct} from 'react-dom/test-utils'
+
+// act is supported [email protected]
+// and is only needed for versions higher than that
+// so we do nothing for versions that don't support act.
+const act = reactAct || (cb => cb())
+
+function rtlAct(...args) {
+  return act(...args)
+}
+
+export default rtlAct

src/index.js

@@ -1,6 +1,11 @@
 import React from 'react'
 import ReactDOM from 'react-dom'
-import {getQueriesForElement, prettyDOM, fireEvent} from 'dom-testing-library'
+import {
+  getQueriesForElement,
+  prettyDOM,
+  fireEvent as dtlFireEvent,
+} from 'dom-testing-library'
+import act from './act-compat'
 
 const mountedContainers = new Set()
 
@@ -21,9 +26,13 @@ function render(
   mountedContainers.add(container)
 
   if (hydrate) {
-    ReactDOM.hydrate(ui, container)
+    act(() => {
+      ReactDOM.hydrate(ui, container)
+    })
   } else {
-    ReactDOM.render(ui, container)
+    act(() => {
+      ReactDOM.render(ui, container)
+    })
   }
   return {
     container,
@@ -65,10 +74,6 @@ function cleanup() {
   mountedContainers.forEach(cleanupAtContainer)
 }
 
-function flushEffects() {
-  ReactDOM.render(null, document.createElement('div'))
-}
-
 // 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) {
@@ -79,6 +84,29 @@ function cleanupAtContainer(container) {
   mountedContainers.delete(container)
 }
 
+// react-testing-library's version of fireEvent will call
+// dom-testing-library's version of fireEvent wrapped inside
+// an "act" call so that after all event callbacks have been
+// been called, the resulting useEffect callbacks will also
+// be called.
+function fireEvent(...args) {
+  let returnValue
+  act(() => {
+    returnValue = dtlFireEvent(...args)
+  })
+  return returnValue
+}
+
+Object.keys(dtlFireEvent).forEach(key => {
+  fireEvent[key] = (...args) => {
+    let returnValue
+    act(() => {
+      returnValue = dtlFireEvent[key](...args)
+    })
+    return returnValue
+  }
+})
+
 // React event system tracks native mouseOver/mouseOut events for
 // running onMouseEnter/onMouseLeave handlers
 // @link https://github.com/facebook/react/blob/b87aabdfe1b7461e7331abb3601d9e6bb27544bc/packages/react-dom/src/events/EnterLeaveEventPlugin.js#L24-L31
@@ -102,6 +130,6 @@ fireEvent.select = (node, init) => {
 
 // just re-export everything from dom-testing-library
 export * from 'dom-testing-library'
-export {render, testHook, cleanup, flushEffects}
+export {render, testHook, cleanup, fireEvent, act}
 
 /* eslint func-name-matching:0 */

typings/index.d.ts

@@ -51,6 +51,8 @@ export function testHook(callback: () => void): void
 export function cleanup(): void
 
 /**
- * Forces React's `useEffect` hook to run synchronously.
+ * Simply calls ReactDOMTestUtils.act(cb)
+ * If that's not available (older version of react) then it
+ * simply calls the given callback immediately
  */
-export function flushEffects(): void
+export function act(callback: () => void): void