Uncaught exceptions from webworkers started by tests in browser runner not shown properly

[jbms]

Describe the bug

When using the browser runner, if a test starts a webworker, and that webworker throws an uncaught exception, instead of the exception being properly printed with other test output, it gets shown as stderr output of "null" with no easy way to track down the source of it.

Reproduction

https://stackblitz.com/edit/vitest-dev-vitest-oszejgfz?file=test%2Fbasic.test.ts

System Info

N/A

See stackblitz.

Used Package Manager

npm

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

[hi-ogawa]

For comparison, here is node worker thread equivalent, which surfaces worker error as unhandled error on main thread https://stackblitz.com/edit/vitest-dev-vitest-izjedp5s?file=test%2Fbasic.test.ts

I think this is a fundamental difference for how error are serialized back to main thread on browser and on node, so I'm not sure there's anything we can do.

Probably the reason why null shows up but not causing "unhandled error test failure" is because null is specifically skipped here.

vitest/packages/browser/src/client/tester/unhandled.ts

Lines 24 to 31 in c82387d

	function throwUnhandlerError(e: ErrorEvent) {
	if (userErrorListenerCount === 0 && e.error != null) {
	cb(e)
	}
	else {
	console.error(e.error)
	}
	}

If you want to resurface worker error as test unhandled errort, this might be possible in user land at least.
https://stackblitz.com/edit/vitest-dev-vitest-w4jcm4z1?file=test%2Fbasic.test.ts

  worker.onerror = (e) => {
    e.stopImmediatePropagation(); // skip `window.on("error" ...)`
    console.error('worker.onerror', e.error);
    throw new Error("Worker error", { cause: e })
  };