Vitest 3 - Freeze/out of memory error with useFakeTimers after upgrade

[rChaoz]

Describe the bug

I'm facing an out-of-memory error of some of my tests right after upgrading to Vitest 3.

Reproduction

This is a simple test that causes it:

import { vi, expect, test } from 'vitest'

vi.useFakeTimers({ now: Date.now() })

test("test", async () => {
    const response = new Response(JSON.stringify({ success: false, message: "forbidden" }), { status: 403 })
    await expect(response.json()).resolves.toMatchInlineSnapshot()
})

Stackblitz - instead of OOM, it will run forever/freeze instead. Locally it will run for 20-60s and crash with OOM, I guess depending on your PC/RAM/whatever

Stacktrace/output

Error: Worker exited unexpectedly
    at ChildProcess.<anonymous> (file:///C:/Users/Matei/Programming/Web%20projects/todo-boards/node_modules/tinypool/dist/index.js:139:34)
    at ChildProcess.emit (node:events:531:35)
    at ChildProcess._handle.onexit (node:internal/child_process:294:12)

<--- Last few GCs --->

[5432:000001AD7D4D0080]    48925 ms: Mark-Compact 4054.3 (4137.8) -> 4041.3 (4140.8) MB, 996.29 / 0.00 ms  (average mu = 0.458, current mu = 0.012) allocation failure; scavenge might not succeed
[5432:000001AD7D4D0080]    50660 ms: Mark-Compact 4057.6 (4141.3) -> 4044.8 (4144.3) MB, 1724.07 / 0.00 ms  (average mu = 0.233, current mu = 0.007) allocation failure; scavenge might not succeed


<--- JS stacktrace --->

FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory
----- Native stack trace -----

 1: 00007FF73629EEDB node::SetCppgcReference+18123
 2: 00007FF736210C34 DSA_meth_get_flags+89940
 3: 00007FF736C87A71 v8::Isolate::ReportExternalAllocationLimitReached+65
 4: 00007FF736C711C8 v8::Function::Experimental_IsNopFunction+1336
 5: 00007FF736AD2C70 v8::Platform::SystemClockTimeMillis+659328
 6: 00007FF736ACFCF8 v8::Platform::SystemClockTimeMillis+647176
 7: 00007FF736AE500A v8::Platform::SystemClockTimeMillis+733978
 8: 00007FF736AE5887 v8::Platform::SystemClockTimeMillis+736151
 9: 00007FF736AF417F v8::Platform::SystemClockTimeMillis+795791
10: 00007FF7367B4865 v8::CodeEvent::GetFunctionName+116773
11: 00007FF736D393FE v8::PropertyDescriptor::writable+678094
12: 00007FF6B6F95830 

Failure cause not provided for 'test'

System info - probably not relevant

System:
    OS: Windows 11 10.0.22631
    CPU: (20) x64 12th Gen Intel(R) Core(TM) i7-12700KF
    Memory: 14.09 GB / 31.86 GB
  Binaries:
    Node: 20.15.1 - C:\Program Files\nodejs\node.EXE
    Yarn: 4.6.0 - C:\Program Files\nodejs\yarn.CMD
    npm: 10.7.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Chromium (127.0.2651.74)
    Internet Explorer: 11.0.22621.3527
  npmPackages:
    @vitest/coverage-v8: 3.0.2 => 3.0.2 
    @vitest/ui: 3.0.2 => 3.0.2 
    vite: 5.4.11 => 5.4.11 
    vitest: ^3.0.2 => 3.0.2

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]

This is likely due to the breaking change of fake timer https://vitest.dev/guide/migration.html#fake-timers-defaults

undici (Node's fetch implementation) seems to use queueMicrotask internally and that one is mocked in Vitest 3 by default. You can configure toFake explicitly to avoid mocking queueMicrotask as explained in the doc.
https://stackblitz.com/edit/vitest-dev-vitest-bmskququ?file=test%2Fbasic.test.ts

(OOM is obviously bad in any case, but I'm not sure if there's anything Vitest can do.)

[rChaoz]

I understand that, but still I think something is fundamentally wrong here - the test has nothing to do with timers. I don't think responses not working should be the intended behaviour, if so there should be a big bold disclaimer in docs about this. Even then, it should tell me, not crash with OOM error that was very hard to pinpoint to this.

[hi-ogawa]

For reference, "mock everything available by default" was also a general direction of the underlying library @sinonjs/fake-timers, but it looks like they also have some reports due to such change:

• Iterating over Readable streams never resolves with fake timers sinonjs/sinon#2619
• Add more specific information in the migration guide to v19 about Fake Timers and toFake sinonjs/sinon#2620
• Node.js can just exit with 0 exit code when all timers mocked as per new default sinonjs/fake-timers#507

[rChaoz]

For anyone experiencing anything similar, I just tested and indeed adding the config for the fake timers fixes this:

fakeTimers: {
    toFake: ["Date", "setTimeout", "clearTimeout"],
},