Reporting regression in V4: incorrect per-test duration with `concurrent`

[dbousamra]

Describe the bug

After upgrading from Vitest v3 to v4, there are two issues:

1. Incorrect test duration reporting

• Tests that clearly run sequentially (~10s each) are reported as taking ~20s each.
• The total suite duration is correct, but per-test timings are inflated.

2. Perceived performance regression

• Our full test suite (~300 tests) increased from ~42s (v3) to ~166s (v4).
• This appears unrelated to the reporting issue, but may be connected to concurrency changes in v4.

Expected:

• Each test should report its actual execution time (~10s in the example).
• Test runtime should remain roughly consistent with v3 under equivalent config.

Actual:

• Each test reports the total elapsed time of the suite segment (~20s).
• Suite runtime is significantly slower in v4.

Reproduction

import { describe, it } from 'vitest';

const delay = (ms: number) => new Promise((r) => setTimeout(r, ms));

describe.concurrent('Blah', () => {
  it('1', async () => {
    console.log('Started test 1');
    await delay(10000);
    console.log('Finished test 1');
  });

  it('2', async () => {
    console.log('Started test 2');
    await delay(10000);
    console.log('Finished test 2');
  });
});

Vitest config:

import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    include: ['tests/**/*.test.ts'],
    maxConcurrency: 1,
    maxWorkers: 1,
  },
});

Observed output:

Started test 1
Finished test 1
Started test 2
Finished test 2

✓ 1  ~20s
✓ 2  ~20s

Even though each test only waits 10s.

Full reproduction (StackBlitz):
https://stackblitz.com/edit/vitest-dev-vitest-1p3gv87f?file=vite.config.ts

System Info

System:
    OS: macOS 26.3
    CPU: (18) arm64 Apple M5 Pro
    Memory: 447.06 MB / 48.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.0.2 - /Users/dbousamra/.nvm/versions/node/v24.0.2/bin/node
    Yarn: 3.5.1 - /opt/homebrew/bin/yarn
    npm: 11.3.0 - /Users/dbousamra/.nvm/versions/node/v24.0.2/bin/npm
    pnpm: 10.11.0 - /Users/dbousamra/Library/pnpm/pnpm
    bun: 1.3.3 - /Users/dbousamra/.bun/bin/bun
    Deno: 2.5.6 - /Users/dbousamra/.deno/bin/deno
  Browsers:
    Chrome: 146.0.7680.178
    Firefox: 148.0
    Safari: 26.3

Used Package Manager

yarn

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.

[hi-ogawa]

For 2nd one, #9653 might be the reason. Previously, hooks execution are not constrained by maxConcurrency, but we changed it so that any user code execution are trapped by same promise concurrency limit. Can you provide more detail on your test setup? e.g. config (maxConcurrency, pool, isolate, worker etc), fixture, beforeEach/beforeAll, concurrent usage?

---

#9653 is included since v4.1.0, so you can test v4.0.x to identify.

[hi-ogawa]

I think the first issue is due to #9653. We cannot help the 2nd issue with the information provided. Please create a separate issue with a reproduction.

[dbousamra]

Hi @hi-ogawa.

Thanks for very fast reply.

I will try and get some more info on the 2nd issue.