fix: ensure sequential mock/unmock resolution by hi-ogawa · Pull Request #9830 · vitest-dev/vitest

hi-ogawa · 2026-03-09T10:44:32Z

Description

Resolves https://discord.com/channels/804011606160703521/1480463846253662218/1480481214170402993

Using Promise.all for handling mock and unmock in parallel can cause race condition when multiple mock and unmock of same modules are involved.

The above CI failures is related because it goes through

"first import"
- beforeEach -> doMock
- test -> import
- afterEach -> doUnmock
"second import"
- beforeEach -> doMock
- test -> import
  - 👈 At this step, unmock/mock requests are handled in parallel. If doUnmock processed slower, then module doesn't get mocked and thus module not found.

vitest/test/core/test/unmock-import.test.ts

Lines 4 to 27 in 4107f8e

    
           beforeEach(() => { 
        
             vi.doMock('/data', () => ({ 
        
               data: { 
        
                 state: 'STARTED', 
        
               }, 
        
             })) 
        
           }) 
        
           afterEach(() => { 
        
             vi.doUnmock('/data') 
        
           }) 
        
           test('first import', async () => { 
        
             // @ts-expect-error I know this 
        
             const { data } = await import('/data') 
        
             data.state = 'STOPPED' 
        
             expect(data.state).toBe('STOPPED') 
        
           }) 
        
           test('second import should have been re-mocked', async () => { 
        
             // @ts-expect-error I know this 
        
             const { data } = await import('/data') 
        
             expect(data.state).toBe('STARTED') 
        
           })

  ⎯⎯⎯⎯⎯⎯⎯ Failed Tests 1 ⎯⎯⎯⎯⎯⎯⎯
   FAIL   threads  test/unmock-import.test.ts:23:1 > second import should have been re-mocked
  Error: Cannot find module '/data'
   ❯ test/unmock-import.test.ts:25:20
       23| test('second import should have been re-mocked', async () => {
       24|   // @ts-expect-error I know this
       25|   const { data } = await import('/data')
         |                    ^
       26|   expect(data.state).toBe('STARTED')
       27| })
  ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯[1/1]⎯

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sheremet-va · 2026-03-10T08:44:19Z

Could we still have it in parallel if all of them are of the same type? (mock/unmock) I feel like this can hit performance hard otherwise.

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hi-ogawa · 2026-03-10T10:17:43Z

That optimization should work fine. Just Claude pushed weird code, so don't look that yet 🙃

Resolve mock/unmock operations in parallel when all pending operations are of the same type. Fall back to sequential resolution when there's a mix to preserve ordering correctness. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

…lution

packages/vitest/src/runtime/moduleRunner/bareModuleMocker.ts

…lution Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

… sequential Group consecutive pending mocks by action type (mock/unmock) and resolve each group in parallel, while running groups sequentially. This avoids unnecessarily serializing all resolutions when a single unmock appears among many mocks. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hi-ogawa added 3 commits March 9, 2026 19:19

fix: ensure sequential mock/unmock resolution

5c6ea68

test: add repro

4107f8e

chore: lint

120e9a7

hi-ogawa marked this pull request as ready for review March 9, 2026 13:44

hi-ogawa mentioned this pull request Mar 10, 2026

soft doesn't work for expect.soft(rejection).resolves #9838

Closed

6 tasks

hi-ogawa force-pushed the 03-09-fix_ensure_sequential_mock_unmock_resolution branch from 253625b to ff15658 Compare March 10, 2026 10:28

hi-ogawa added 3 commits March 10, 2026 19:32

refactor: cleanup

739ff08

Merge branch 'main' into 03-09-fix_ensure_sequential_mock_unmock_reso…

2fbff0b

…lution

Merge branch 'main' into 03-09-fix_ensure_sequential_mock_unmock_reso…

de1a665

…lution

hi-ogawa requested a review from sheremet-va March 11, 2026 01:40

sheremet-va requested changes Mar 19, 2026

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packages/vitest/src/runtime/moduleRunner/bareModuleMocker.ts Outdated Show resolved Hide resolved

hi-ogawa and others added 3 commits March 24, 2026 12:31

Merge branch 'main' into 03-09-fix_ensure_sequential_mock_unmock_reso…

ac29cf7

…lution Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

refactor: nit

e3d8cfe

sheremet-va approved these changes Mar 24, 2026

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sheremet-va merged commit 7c06598 into vitest-dev:main Mar 24, 2026
13 of 16 checks passed

hi-ogawa deleted the 03-09-fix_ensure_sequential_mock_unmock_resolution branch March 24, 2026 08:47

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fix: ensure sequential mock/unmock resolution#9830

fix: ensure sequential mock/unmock resolution#9830
sheremet-va merged 10 commits intovitest-dev:mainfrom
hi-ogawa:03-09-fix_ensure_sequential_mock_unmock_resolution

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	beforeEach(() => {
	vi.doMock('/data', () => ({
	data: {
	state: 'STARTED',
	},
	}))
	})

	afterEach(() => {
	vi.doUnmock('/data')
	})

	test('first import', async () => {
	// @ts-expect-error I know this
	const { data } = await import('/data')
	data.state = 'STOPPED'
	expect(data.state).toBe('STOPPED')
	})

	test('second import should have been re-mocked', async () => {
	// @ts-expect-error I know this
	const { data } = await import('/data')
	expect(data.state).toBe('STARTED')
	})

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Description

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hi-ogawa commented Mar 9, 2026 •

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