v4: inconsistent errors with pool: 'forks' or 'vmForks' #8861
Description
Describe the bug
I have a vue 3/ts/vuetify project with some tests and they break in random places after vitest@4 update. I've found that pool: 'threads' and 'vmThreads' are ok, while pool: 'forks' or 'vmForks' trigger the errors. fileParallelism: false or maxWorkers: 1 make forks work correctly, same as running only one test file.
Not every run ends with errors, sometimes all the tests go well. The errors are like:
SyntaxError: Unexpected end of input
SyntaxError: Unexpected token '}'
SyntaxError: missing ) after argument list
SyntaxError: Missing initializer in const declaration
TypeError: (0 , vite_ssr_import_3.genericComponent) is not a function
TypeError: (0 , vite_ssr_import_2.createVuetify) is not a function
TypeError: (0 , vite_ssr_import_1.createVuetifyAdapter) is not a function
TypeError: (0 , vite_ssr_import_1.createDefaults) is not a function
TypeError: (0 , vite_ssr_import_1.someFunctionFromProjectImportedInTestFile) is not a function
I made a small reproduction, but the smaller the project the harder it is to trigger an error. In the reproduction repo I can get errors after importing the result of createVuetify function in at least 2 test files, or while importing it in 1 test file while using vuetify component in a project component. But in the original project the errors are reproducible even when running a subset of the test files for simple functions, so it doesn't look like a vuetify problem
Reproduction
https://github.com/its2easy/vitest4-error
Run npm test or npm run test:50 to run the tests 50 times in a row (sometimes the error may appear 1/2 runs, and sometimes it's 1/30)
btw I couldn't reproduce the errors on StackBlitz
System Info
System:
OS: Windows 11 10.0.26100
CPU: (16) x64 AMD Ryzen 7 4800H with Radeon Graphics
Memory: 14.13 GB / 31.37 GB
Binaries:
Node: 24.10.0 - C:\Program Files\nodejs\node.EXE
npm: 11.6.1 - C:\Program Files\nodejs\npm.CMD
Browsers:
Chrome: 141.0.7390.108
Edge: Chromium (140.0.3485.54)
Firefox: 144.0.2 - C:\Program Files\Mozilla Firefox\firefox.exe
Internet Explorer: 11.0.26100.1882Used Package Manager
npm
Validations
- Follow our Code of Conduct
- Read the Contributing Guidelines.
- Read the docs.
- Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
- Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
- The provided reproduction is a minimal reproducible example of the bug.