Add SSR test for serverState behavior

jest.config.js

@@ -13,7 +13,7 @@ const tsTestFolderPath = (folderName) =>
 
 const tsStandardConfig = {
   ...defaults,
-  displayName: 'ReactDOM 18',
+  displayName: 'ReactDOM 18 (Shim)',
   preset: 'ts-jest',
   testMatch: NORMAL_TEST_FOLDERS.map(tsTestFolderPath),
 }
@@ -42,7 +42,7 @@ const standardReact17Config = {
 
 const nextEntryConfig = {
   ...tsStandardConfig,
-  displayName: 'Next',
+  displayName: 'ReactDOM 18 (Next)',
   moduleNameMapper: {
     '../../src/index': '<rootDir>/src/next',
   },

test/components/connect.spec.tsx

@@ -530,9 +530,7 @@ describe('React', () => {
 
         const ConnectedInner = connect(
           (state) => ({ stateThing: state }),
-          (dispatch) => ({
-            doSomething: (whatever: any) => dispatch(doSomething(whatever)),
-          }),
+          { doSomething },
           (stateProps, actionProps, parentProps: InnerPropsType) => ({
             ...stateProps,
             ...actionProps,

test/integration/ssr.spec.tsx

@@ -0,0 +1,202 @@
+import React, { Suspense, useState, useEffect } from 'react'
+import * as rtl from '@testing-library/react'
+import { renderToString } from 'react-dom/server'
+import { hydrateRoot } from 'react-dom/client'
+import { createStore, createSlice, PayloadAction } from '@reduxjs/toolkit'
+import {
+  Provider,
+  connect,
+  useSelector,
+  useDispatch,
+  ConnectedProps,
+} from '../../src/index'
+
+const IS_REACT_18 = React.version.startsWith('18')
+
+describe('New v8 serverState behavior', () => {
+  interface State {
+    count: number
+    data: string[]
+  }
+  const initialState: State = {
+    count: 0,
+    data: [],
+  }
+
+  const dataSlice = createSlice({
+    name: 'data',
+    initialState,
+    reducers: {
+      fakeLoadData(state, action: PayloadAction<string>) {
+        state.data.push(action.payload)
+      },
+      increaseCount(state) {
+        state.count++
+      },
+    },
+  })
+
+  const { fakeLoadData, increaseCount } = dataSlice.actions
+
+  const selectCount = (state: State) => state.count
+
+  function useIsHydrated() {
+    // Get weird Babel-errors when I try to destruct arrays..
+    const hydratedState = useState(false)
+    const hydrated = hydratedState[0]
+    const setHydrated = hydratedState[1]
+
+    // When this effect runs and the component being hydrated isn't
+    // exactly the same thing but close enough for this demo.
+    useEffect(() => {
+      setHydrated(true)
+    }, [setHydrated])
+
+    return hydrated
+  }
+
+  function GlobalCountButton() {
+    const isHydrated = useIsHydrated()
+    const count = useSelector(selectCount)
+    const dispatch = useDispatch()
+
+    return (
+      <button
+        disabled={!isHydrated}
+        style={{ marginLeft: '24px' }}
+        onClick={() => dispatch(increaseCount())}
+      >
+        useSelector:
+        {isHydrated
+          ? `Hydrated. Count: ${count}`
+          : `Not hydrated. Count: ${count}`}
+      </button>
+    )
+  }
+
+  const mapState = (state: State) => ({
+    count: selectCount(state),
+  })
+
+  const gcbConnector = connect(mapState)
+  type PropsFromRedux = ConnectedProps<typeof gcbConnector>
+
+  function GlobalCountButtonConnect({ count, dispatch }: PropsFromRedux) {
+    const isHydrated = useIsHydrated()
+
+    return (
+      <button
+        disabled={!isHydrated}
+        style={{ marginLeft: '24px' }}
+        onClick={() => dispatch(increaseCount())}
+      >
+        Connect:
+        {isHydrated
+          ? `Hydrated. Count: ${count}`
+          : `Not hydrated. Count: ${count}`}
+      </button>
+    )
+  }
+
+  const ConnectedGlobalCountButtonConnect = gcbConnector(
+    GlobalCountButtonConnect
+  )
+
+  function App() {
+    return (
+      <div>
+        <Suspense fallback={<Spinner />}>
+          <GlobalCountButton />
+          <ConnectedGlobalCountButtonConnect />
+        </Suspense>
+      </div>
+    )
+  }
+
+  const Spinner = () => <div />
+
+  if (!IS_REACT_18) {
+    it('Dummy test for React 17, ignore', () => {})
+    return
+  }
+
+  let consoleError = jest.spyOn(console, 'error').mockImplementation(() => {})
+
+  afterEach(() => {
+    jest.clearAllMocks()
+  })
+
+  it.only('Handles hydration correctly', async () => {
+    const ssrStore = createStore(dataSlice.reducer)
+
+    // Simulating loading all data before rendering the app
+    ssrStore.dispatch(fakeLoadData("Wait, it doesn't wait for React to load?"))
+    ssrStore.dispatch(fakeLoadData('How does this even work?'))
+    ssrStore.dispatch(fakeLoadData('I like marshmallows'))
+
+    const markup = renderToString(
+      <Provider store={ssrStore}>
+        <App />
+      </Provider>
+    )
+
+    // Pretend we have server-rendered HTML
+    const rootDiv = document.createElement('div')
+    document.body.appendChild(rootDiv)
+    rootDiv.innerHTML = markup
+
+    const initialState = ssrStore.getState()
+    const clientStore = createStore(dataSlice.reducer, initialState)
+
+    // Intentionally update client store to change state vs server
+    clientStore.dispatch(increaseCount())
+
+    // First hydration attempt with just the store should fail due to mismatch
+    await rtl.act(async () => {
+      hydrateRoot(
+        rootDiv,
+        <Provider store={clientStore}>
+          <App />
+        </Provider>
+      )
+    })
+
+    const [lastCall = []] = consoleError.mock.calls.slice(-1)
+    const [errorArg] = lastCall
+    expect(errorArg).toBeInstanceOf(Error)
+    expect(/There was an error while hydrating/.test(errorArg.message)).toBe(
+      true
+    )
+
+    jest.resetAllMocks()
+
+    expect(consoleError.mock.calls.length).toBe(0)
+
+    document.body.removeChild(rootDiv)
+
+    const clientStore2 = createStore(dataSlice.reducer, initialState)
+    clientStore2.dispatch(increaseCount())
+
+    const rootDiv2 = document.createElement('div')
+    document.body.appendChild(rootDiv2)
+    rootDiv2.innerHTML = markup
+
+    // Second attempt should pass, because we provide serverState
+    await rtl.act(async () => {
+      hydrateRoot(
+        rootDiv2,
+        <Provider store={clientStore2} serverState={initialState}>
+          <App />
+        </Provider>
+      )
+    })
+
+    expect(consoleError.mock.calls.length).toBe(0)
+
+    // Buttons should both exist, and have the updated count due to later render
+    const button1 = rtl.screen.getByText('useSelector:Hydrated. Count: 1')
+    expect(button1).not.toBeNull()
+    const button2 = rtl.screen.getByText('Connect:Hydrated. Count: 1')
+    expect(button2).not.toBeNull()
+  })
+})