feat: Use concurrent React when available

.github/workflows/validate.yml

@@ -16,6 +16,7 @@ jobs:
     # ignore all-contributors PRs
     if: ${{ !contains(github.head_ref, 'all-contributors') }}
     strategy:
+      fail-fast: false
       matrix:
         node: [12, 14, 16]
         react: [latest, next, experimental]
@@ -47,6 +48,8 @@ jobs:
 
       - name: ⬆️ Upload coverage report
         uses: codecov/codecov-action@v1
+        with:
+          flags: ${{ matrix.react }}
 
   release:
     needs: main

jest.config.js

@@ -0,0 +1,15 @@
+const {jest: jestConfig} = require('kcd-scripts/config')
+
+module.exports = Object.assign(jestConfig, {
+  coverageThreshold: {
+    ...jestConfig.coverageThreshold,
+    // full coverage across the build matrix (React 17, 18) but not in a single job
+    './src/pure': {
+      // minimum coverage of jobs using React 17 and 18
+      branches: 85,
+      functions: 76,
+      lines: 81,
+      statements: 81,
+    },
+  },
+})

src/__tests__/cleanup.js

@@ -83,10 +83,7 @@ describe('fake timers and missing act warnings', () => {
     expect(microTaskSpy).toHaveBeenCalledTimes(0)
     // console.error is mocked
     // eslint-disable-next-line no-console
-    expect(console.error).toHaveBeenCalledTimes(
-      // ReactDOM.render is deprecated in React 18
-      React.version.startsWith('18') ? 1 : 0,
-    )
+    expect(console.error).toHaveBeenCalledTimes(0)
   })
 
   test('cleanup does not swallow missing act warnings', () => {
@@ -118,16 +115,10 @@ describe('fake timers and missing act warnings', () => {
     expect(deferredStateUpdateSpy).toHaveBeenCalledTimes(1)
     // console.error is mocked
     // eslint-disable-next-line no-console
-    expect(console.error).toHaveBeenCalledTimes(
-      // ReactDOM.render is deprecated in React 18
-      React.version.startsWith('18') ? 2 : 1,
-    )
+    expect(console.error).toHaveBeenCalledTimes(1)
     // eslint-disable-next-line no-console
-    expect(
-      console.error.mock.calls[
-        // ReactDOM.render is deprecated in React 18
-        React.version.startsWith('18') ? 1 : 0
-      ][0],
-    ).toMatch('a test was not wrapped in act(...)')
+    expect(console.error.mock.calls[0][0]).toMatch(
+      'a test was not wrapped in act(...)',
+    )
   })
 })

src/__tests__/end-to-end.js

@@ -1,5 +1,5 @@
 import * as React from 'react'
-import {render, waitForElementToBeRemoved, screen} from '../'
+import {render, waitForElementToBeRemoved, screen, waitFor} from '../'
 
 const fetchAMessage = () =>
   new Promise(resolve => {
@@ -29,9 +29,37 @@ class ComponentWithLoader extends React.Component {
   }
 }
 
-test('it waits for the data to be loaded', async () => {
-  render(<ComponentWithLoader />)
-  const loading = () => screen.getByText('Loading...')
-  await waitForElementToBeRemoved(loading)
-  expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
+describe.each([
+  ['real timers', () => jest.useRealTimers()],
+  ['fake legacy timers', () => jest.useFakeTimers('legacy')],
+  ['fake modern timers', () => jest.useFakeTimers('modern')],
+])('it waits for the data to be loaded using %s', (label, useTimers) => {
+  beforeEach(() => {
+    useTimers()
+  })
+
+  afterEach(() => {
+    jest.useRealTimers()
+  })
+
+  test('waitForElementToBeRemoved', async () => {
+    render(<ComponentWithLoader />)
+    const loading = () => screen.getByText('Loading...')
+    await waitForElementToBeRemoved(loading)
+    expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
+  })
+
+  test('waitFor', async () => {
+    render(<ComponentWithLoader />)
+    const message = () => screen.getByText(/Loaded this message:/)
+    await waitFor(message)
+    expect(screen.getByTestId('message')).toHaveTextContent(/Hello World/)
+  })
+
+  test('findBy', async () => {
+    render(<ComponentWithLoader />)
+    await expect(screen.findByTestId('message')).resolves.toHaveTextContent(
+      /Hello World/,
+    )
+  })
 })

src/__tests__/new-act.js

@@ -1,4 +1,4 @@
-let asyncAct, consoleErrorMock
+let asyncAct
 
 jest.mock('react-dom/test-utils', () => ({
   act: cb => {
@@ -9,11 +9,11 @@ jest.mock('react-dom/test-utils', () => ({
 beforeEach(() => {
   jest.resetModules()
   asyncAct = require('../act-compat').asyncAct
-  consoleErrorMock = jest.spyOn(console, 'error').mockImplementation(() => {})
+  jest.spyOn(console, 'error').mockImplementation(() => {})
 })
 
 afterEach(() => {
-  consoleErrorMock.mockRestore()
+  console.error.mockRestore()
 })
 
 test('async act works when it does not exist (older versions of react)', async () => {

src/__tests__/old-act.js

@@ -1,13 +1,13 @@
-let asyncAct, consoleErrorMock
+let asyncAct
 
 beforeEach(() => {
   jest.resetModules()
   asyncAct = require('../act-compat').asyncAct
-  consoleErrorMock = jest.spyOn(console, 'error').mockImplementation(() => {})
+  jest.spyOn(console, 'error').mockImplementation(() => {})
 })
 
 afterEach(() => {
-  consoleErrorMock.mockRestore()
+  console.error.mockRestore()
 })
 
 jest.mock('react-dom/test-utils', () => ({

src/__tests__/render.js

@@ -101,3 +101,36 @@ test('flushes useEffect cleanup functions sync on unmount()', () => {
 
   expect(spy).toHaveBeenCalledTimes(1)
 })
+
+test('throws if `legacyRoot: false` is used with an incomaptible version', () => {
+  const isConcurrentReact = typeof ReactDOM.createRoot === 'function'
+
+  const performConcurrentRender = () => render(<div />, {legacyRoot: false})
+
+  // eslint-disable-next-line jest/no-if -- jest doesn't support conditional tests
+  if (isConcurrentReact) {
+    // eslint-disable-next-line jest/no-conditional-expect -- yes, jest still doesn't support conditional tests
+    expect(performConcurrentRender).not.toThrow()
+  } else {
+    // eslint-disable-next-line jest/no-conditional-expect -- yes, jest still doesn't support conditional tests
+    expect(performConcurrentRender).toThrowError(
+      `Attempted to use concurrent React with \`react-dom@${ReactDOM.version}\`. Be sure to use the \`next\` or \`experimental\` release channel (https://reactjs.org/docs/release-channels.html).`,
+    )
+  }
+})
+
+test('can be called multiple times on the same container', () => {
+  const container = document.createElement('div')
+
+  const {unmount} = render(<strong />, {container})
+
+  expect(container).toContainHTML('<strong></strong>')
+
+  render(<em />, {container})
+
+  expect(container).toContainHTML('<em></em>')
+
+  unmount()
+
+  expect(container).toBeEmptyDOMElement()
+})

src/__tests__/stopwatch.js

@@ -53,8 +53,5 @@ test('unmounts a component', async () => {
   // and get an error.
   await sleep(5)
   // eslint-disable-next-line no-console
-  expect(console.error).toHaveBeenCalledTimes(
-    // ReactDOM.render is deprecated in React 18
-    React.version.startsWith('18') ? 1 : 0,
-  )
+  expect(console.error).not.toHaveBeenCalled()
 })