parallel/test-fastutf8stream-flush-mocks and parallel/test-fastutf8stream-sync are flaky on Windows

[joyeecheung]

From https://github.com/nodejs/reliability/blob/main/reports/2025-08-26.md

Reason	parallel/test-fastutf8stream-flush-mocks
Type	JS_TEST_FAILURE
Failed PR	14 (https://github.com/nodejs/node/pull/59567/, https://github.com/nodejs/node/pull/59570/, https://github.com/nodejs/node/pull/59571/, https://github.com/nodejs/node/pull/59350/, https://github.com/nodejs/node/pull/59527/, https://github.com/nodejs/node/pull/59579/, https://github.com/nodejs/node/pull/59595/, https://github.com/nodejs/node/pull/58155/, https://github.com/nodejs/node/pull/58680/, https://github.com/nodejs/node/pull/59601/, https://github.com/nodejs/node/pull/58797/, https://github.com/nodejs/node/pull/59576/, https://github.com/nodejs/node/pull/59179/, https://github.com/nodejs/node/pull/59603/)
Appeared	test-rackspace-win2016_vs2015-x64-1, test-rackspace-win2016_vs2015-x64-2, test-azure_msft-win2016_vs2017-x64-1
First CI	https://ci.nodejs.org/job/node-test-pull-request/68781/
Last CI	https://ci.nodejs.org/job/node-test-pull-request/68867/

Example

not ok 319 parallel/test-fastutf8stream-flush-mocks
  ---
  duration_ms: 928.99500
  severity: fail
  exitcode: 1
  stack: |-
    Can't clean tmpdir: C:\workspace\node-test-binary-windows-js-suites\node\test\.tmp.302
    Files blocking: [
      'fastutf8stream-2252-1756150137626-0.log',
      'fastutf8stream-2252-1756150137632-2.log'
    ]
    
    C:\workspace\node-test-binary-windows-js-suites\node\test\common\tmpdir.js:80
        throw e;
        ^
    
    Error: ENOTEMPTY: directory not empty, rmdir 'C:\workspace\node-test-binary-windows-js-suites\node\test\.tmp.302'
        at Object.rmdirSync (node:fs:1206:11)
        at _rmdirSync (node:internal/fs/rimraf:261:21)
        at rimrafSync (node:internal/fs/rimraf:194:7)
        at Object.rmSync (node:fs:1252:10)
        at rmSync (C:\workspace\node-test-binary-windows-js-suites\node\test\common\tmpdir.js:31:8)
        at onexit (C:\workspace\node-test-binary-windows-js-suites\node\test\common\tmpdir.js:65:5)
        at process.<anonymous> (C:\workspace\no...

---

Reason	parallel/test-fastutf8stream-sync
Type	JS_TEST_FAILURE
Failed PR	14 (https://github.com/nodejs/node/pull/59567/, https://github.com/nodejs/node/pull/59570/, https://github.com/nodejs/node/pull/59571/, https://github.com/nodejs/node/pull/59350/, https://github.com/nodejs/node/pull/59527/, https://github.com/nodejs/node/pull/59579/, https://github.com/nodejs/node/pull/59595/, https://github.com/nodejs/node/pull/58155/, https://github.com/nodejs/node/pull/58680/, https://github.com/nodejs/node/pull/59601/, https://github.com/nodejs/node/pull/58797/, https://github.com/nodejs/node/pull/59576/, https://github.com/nodejs/node/pull/59179/, https://github.com/nodejs/node/pull/59603/)
Appeared	test-rackspace-win2016_vs2015-x64-2, test-azure_msft-win2016_vs2017-x64-2
First CI	https://ci.nodejs.org/job/node-test-pull-request/68781/
Last CI	https://ci.nodejs.org/job/node-test-pull-request/68867/

Example

not ok 314 parallel/test-fastutf8stream-sync
  ---
  duration_ms: 1050.01600
  severity: fail
  exitcode: 1
  stack: |-
    Can't clean tmpdir: C:\workspace\node-test-binary-windows-js-suites\node\test\.tmp.304
    Files blocking: [
      'fastutf8stream-4936-1756150148470-2.log',
      'fastutf8stream-4936-1756150148534-7.log'
    ]
    
    C:\workspace\node-test-binary-windows-js-suites\node\test\common\tmpdir.js:80
        throw e;
        ^
    
    Error: ENOTEMPTY: directory not empty, rmdir 'C:\workspace\node-test-binary-windows-js-suites\node\test\.tmp.304'
        at Object.rmdirSync (node:fs:1206:11)
        at _rmdirSync (node:internal/fs/rimraf:261:21)
        at rimrafSync (node:internal/fs/rimraf:194:7)
        at Object.rmSync (node:fs:1252:10)
        at rmSync (C:\workspace\node-test-binary-windows-js-suites\node\test\common\tmpdir.js:31:8)
        at onexit (C:\workspace\node-test-binary-windows-js-suites\node\test\common\tmpdir.js:65:5)
        at process.<anonymous> (C:\workspace\node-tes...

These tests were introduced in #58897

[mcollina]

cc @jasnell

I'll also see if I can give it a go. The solution is to keep retrying until it's possible to delete the files (yes, unfortunately).

Windows filesystem is very hard to work with.

[joyeecheung]

These are happening in the onexit handler for tmpdir, which aren't happening in many other files that also use tmpdir, so I am inclined to think that it's a problem with the test (it might be still writing before the process is about to shut down or something), less so with the tmpdir thing.

[mcollina]

Closing as those flakes are no longer happening: #59667 (comment).