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Two @tanstack/db tests time out under CPU load because a cold module import counts against the 5 s default timeout

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
82/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
typescript
Domain
testing

Research direction

Read packages/db/tests/mutation-id.test.ts and packages/db/tests/collection-idle-cleanup.test.ts, then run the two-file Vitest command from packages/db under CPU load to confirm the timeouts. Check how each test imports the Collection module graph and handles setup; the idle-cleanup scheduler must be installed before its polyfill import. Done when both tests reliably pass under load without weakening their assertions.

Written by the indexing model from the issue text.

Description

Two @tanstack/db tests fail with Test timed out in 5000ms when the machine is busy. They pass when the suite runs alone.

Tests

  • packages/db/tests/mutation-id.test.ts > mutation ids > do not draw random values during module evaluation
  • packages/db/tests/collection-idle-cleanup.test.ts > cancels a rescheduled idle cleanup when a subscriber returns

Reproduction

Run the two files while other test processes load the CPU. I ran them while four other vitest run processes ran the full @tanstack/db suite on an 18-core machine:

cd packages/db
npx vitest run tests/mutation-id.test.ts tests/collection-idle-cleanup.test.ts

Result over four runs:

Run mutation-id collection-idle-cleanup
1 timed out (5005 ms) timed out (5014 ms)
2 timed out (5003 ms) timed out (5004 ms)
3 timed out (5004 ms) timed out (5004 ms)
4 timed out (5004 ms) passed

Without the other processes, the full suite passes (285 files, 13,816 tests).

Probable cause

Each test starts with a cold dynamic import() of the Collection module graph inside the test body:

  • mutation-id.test.ts calls vi.resetModules() and then imports ../src/collection/index.js and ../src/local-only.js.
  • collection-idle-cleanup.test.ts imports ../src/collection/index.js and ../src/utils/browser-polyfills.js, because it must install its idle scheduler before the polyfill module loads.

The transform and load of that graph count against the test's 5000 ms default timeout. Under CPU load, the import alone can use the full budget. The work after the import takes a few milliseconds, plus an 80 ms wait in the idle-cleanup test.

I did not measure the import time separately, so this cause is probable, not proven.

Effect

  • A slow or shared CI runner can fail these tests for no product reason.
  • Tools that run the suite in parallel, such as mutation sweeps, record false failures. Both tests made a mutation sweep report every mutant as killed.

Possible fixes

  • Give each test an explicit timeout that covers a cold import, for example 30_000.
  • Or move the import out of the timed test body where the test's isolation requirement allows it. The idle-cleanup test needs its scheduler installed before the polyfill module loads, so its import must stay after that setup.
Dominant language
TypeScript
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Merged PRs (30d)
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