upgrading @vitest/browser completely breaks tests

[m-lyon]

Describe the bug

I recently upgraded from vitest 2.x to 3.x, and in doing so updated @vitest/browser to 3.1.1 from 2.1.8. In doing so, this bumped the requirement for @testing-library/user-event from ^14.5.2 to ^14.6.1. This change in @testing-library/user-event has broken all of my (non browser mode) tests.

An example of an error is:

Error: Should not already be working.
 ❯ performSyncWorkOnRoot node_modules/react-dom/cjs/react-dom.development.js:26112:11
 ❯ flushSyncCallbacks node_modules/react-dom/cjs/react-dom.development.js:12042:22
 ❯ flushActQueue node_modules/react/cjs/react.development.js:2667:24
 ❯ act node_modules/react/cjs/react.development.js:2582:11
 ❯ node_modules/@testing-library/react/dist/act-compat.js:47:25
 ❯ node_modules/@testing-library/react/dist/pure.js:285:28
 ❯ cleanup node_modules/@testing-library/react/dist/pure.js:281:22
 ❯ src/features/recipeIngredient/components/__tests__/EditableIngredient.test.tsx:15:9
     13| describe('Dropdown Action Keyboard', () => {
     14|     afterEach(() => {
     15|         cleanup();
       |         ^
     16|     });
     17|     it('should not navigate below dropdown options', async () => {

and dialog in the @vitest/ui shows

Warning: Attempted to synchronously unmount a root while React was already rendering. React cannot finish unmounting the root until the current render has completed, which may lead to a race condition.

Reproduction

The errors can be recreated in this repository commit by running npm run test.

I've had an initial go at trying to recreate this bug on a stackblitz but wasn't able to. If this is not a minimal enough of an example I can spend some time trying to do that.

For reference, this commit is one where the tests are working, where only the @testing-library/user-event requirement has been changed.

System Info

System:
    OS: Linux 6.8 Ubuntu 24.04.2 LTS 24.04.2 LTS (Noble Numbat)
    CPU: (12) x64 AMD Ryzen 5 5600X 6-Core Processor
    Memory: 18.30 GB / 31.25 GB
    Container: Yes
    Shell: 5.2.21 - /bin/bash
  Binaries:
    Node: 20.19.0 - ~/.nvm/versions/node/v20.19.0/bin/node
    npm: 10.8.2 - ~/.nvm/versions/node/v20.19.0/bin/npm
  Browsers:
    Chrome: 131.0.6778.85
  npmPackages:
    @vitest/browser: ^3.1.1 => 3.1.1 
    @vitest/ui: ^3.1.1 => 3.1.1 
    playwright: ^1.49.1 => 1.49.1 
    vite: ^6.2.5 => 6.2.5 
    vitest: ^3.1.1 => 3.1.1 
    vitest-browser-react: ^0.1.1 => 0.1.1 
    vitest-fetch-mock: ^0.4.5 => 0.4.5

Used Package Manager

npm

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[hi-ogawa]

Yes, please try reducing the reproduction. From the description, I'm not sure how we see this as Vitest bug than @testing-library/user-event bug (or any testing-library family).

[github-actions]

Hello @m-lyon. Please provide a minimal reproduction using a GitHub repository or StackBlitz (you can also use examples). Issues marked with needs reproduction will be closed if they have no activity within 3 days.