Forks pool `stdout` not piped to main process

[AriPerkkio]

Describe the bug

Summary reporter is unable to capture stdout of forks pool's runners. This messes up the re-rendering as whole stream is not handled.

It's same issue as:

• fix(child_process): pipe stdout and stderr to main thread tinylibs/tinypool#104

Reproduction

Vitest monorepo, test/coverage-test with pool: 'forks'.

System Info

Vitest monorepo, Node 22.

Used Package Manager

pnpm

Validations

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• The provided reproduction is a minimal reproducible example of the bug.

[ThiloAschebrock]

An observation of mine that might be related: I am seeing a couple of MaxListenersExceededWarning (same error as reported at #7194) after the upgrade to vitest 4 when running my tests that include v8 coverage with the default pool option fork. Switching to pool option thread resolves the issue.

[AriPerkkio]

Can you show the full error you are getting @ThiloAschebrock? Is the error about abort signals or exit code listeners?

[ThiloAschebrock]

After the tests are running for a while, I can see this message pop up multiple times in the output of the tests:

(node:4728) MaxListenersExceededWarning: Possible EventTarget memory leak detected. 11 message listeners added to [MessagePort [EventTarget]]. MaxListeners is 10. Use events.setMaxListeners() to increase limit                                                                                   

(Use `node --trace-warnings ...` to show where the warning was created)   

Are you interested in the trace output?

[AriPerkkio]

Those warnings are not related to this issue. They were fixed in:

• fix(pool): runner's error listener causing MaxListenersExceededWarning #8820
• fix(worker): rpc listener leak when isolate: false #8821

They will be included in the next patch release.