Using test.concurrent causes test report to attribute console output incorrectly

[wenninger-stephan]

Hi!

We are using Vitest in a larger project and I noticed that when using test.concurrent, the resulting test report (we are using junit xml format) incorrectly attributes the console outputs to the respective tests. Some console output is even missing completely, however only from the test report file, we are also using the default reporter, and when we pipe its console output to a file, we can see all console output (however also not attributed to the correct test).

Are the test reporters supposed to handle test.concurrent? Are we missing some setting that is needed for this to work?

Reproduction is given below:

package.json

{
  "name": "vitest-concurrent",
  "version": "1.0.0",
  "description": "Sample for concurrent vitest tests",
  "main": "index.js",
  "scripts": {
    "test": "vitest",
    "test:ci": "vitest run"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "vitest": "^4.0.15"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "target": "ESNext",
    "module": "ESNext",
    "outDir": "./dist",
    "sourceMap": true,
    "moduleResolution": "node",
    "strict": true
  },
  "include": ["test"]
}

test/concurrent.test.ts

import { expect, test } from 'vitest';

for (let i = 0; i < 6; ++i) {
  test.concurrent(`ConcurrentTestCase${i}`, ({ expect }) => {
    console.log(`Running concurrent test ${i}`);
    expect(true).toBe(true);
  });
}

for (let i = 0; i < 6; ++i) {
  test(`SequentialTestCase${i}`, () => {
    console.log(`Running sequential test ${i}`);
    expect(true).toBe(true);
  });
}

running npx vitest run --reporter=default --reporter=junit --outputFile=reports/vitest.junit.xml after npm install shows the behavior. On my machine it results in the following

reports/vitest.junit.xml

<?xml version="1.0" encoding="UTF-8" ?>
<testsuites name="vitest tests" tests="12" failures="0" errors="0" time="0.011120403">
    <testsuite name="test/concurrent.test.ts" timestamp="" hostname="" tests="12" failures="0" errors="0" skipped="0" time="0.011120403">
        <testcase classname="test/concurrent.test.ts" name="ConcurrentTestCase0" time="0.005383724">
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="ConcurrentTestCase1" time="0.004898973">
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="ConcurrentTestCase2" time="0.004843386">
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="ConcurrentTestCase3" time="0.004805191">
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="ConcurrentTestCase4" time="0.004771573">
            <system-out>
Running concurrent test 0
Running concurrent test 1
Running concurrent test 2
Running concurrent test 3
Running concurrent test 4

            </system-out>
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="ConcurrentTestCase5" time="0.000681675">
            <system-out>
Running concurrent test 5

            </system-out>
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="SequentialTestCase0" time="0.000453331">
            <system-out>
Running sequential test 0

            </system-out>
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="SequentialTestCase1" time="0.000342989">
            <system-out>
Running sequential test 1

            </system-out>
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="SequentialTestCase2" time="0.00090061">
            <system-out>
Running sequential test 2

            </system-out>
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="SequentialTestCase3" time="0.000468815">
            <system-out>
Running sequential test 3

            </system-out>
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="SequentialTestCase4" time="0.000259063">
            <system-out>
Running sequential test 4

            </system-out>
        </testcase>
        <testcase classname="test/concurrent.test.ts" name="SequentialTestCase5" time="0.000157254">
            <system-out>
Running sequential test 5

            </system-out>
        </testcase>
    </testsuite>
</testsuites>

Same for the machine of a colleague, so the output seems "deterministic" in that sense.
As you can see, some console output is attributed incorrectly to Test 4 in the concurrent cases.
Is this a (known) bug/limitation?

  System:
    OS: Linux 6.14 Ubuntu 24.04.3 LTS 24.04.3 LTS (Noble Numbat)
    CPU: (16) x64 Intel(R) Core(TM) Ultra 9 285H
    Memory: 14.36 GB / 30.81 GB
    Container: Yes
    Shell: 5.2.21 - /bin/bash
  Binaries:
    Node: 22.18.0 -
    npm: 10.9.3 - 
  Browsers:
    Chrome: 143.0.7499.40
    Firefox: 146.0
    Firefox Developer Edition: 146.0
  npmPackages:
    vitest: ^4.0.15 => 4.0.15 

Thanks a lot!