test: improve flaky test-listen-fd-ebadf.js

[Trott]

Find an invalid file descriptor rather than assuming 42 will be invalid.

Fixes: #17762

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

test net

[Trott]

Ping @gibfahn

[Trott]

CI: https://ci.nodejs.org/job/node-test-pull-request/12238/

[gibfahn]

Seems reasonable, let me try it on the machine that was failing.

[gibfahn]

descripter -> descriptor in the commit message btw

[gibfahn]

$ tools/test.py -J --repeat 1000 parallel/test-listen-fd-ebadfCommand: out/Release/node /dev/shm/gib/node/test/parallel/test-listen-fd-ebadf.js[00:08|% 100|+ 980|- 20]: Done 
$ tools/test.py -J --repeat 1000 parallel/test-listen-fd-ebadf-trott[00:08|% 100|+ 1000|- 0]: Done

Looks like that fixes it, thanks @Trott !

EDIT: Since the machine is idle, why not do a proper stress test:

$ tools/test.py -J --repeat 100000 parallel/test-listen-fd-ebadf-trott[25:31|% 100|+ 100000|- 0]: Done

[Trott]

(CI issues are infra-related, unrelated to this PR.)

[Trott]

Landed in 1d87891

[gibfahn]

Doesn't land cleanly on 6.x. Assuming this test is flaky there too, a backport would be useful.

Diff:

diff --git a/test/parallel/test-listen-fd-ebadf.js b/test/parallel/test-listen-fd-ebadf.js
index dfa99e274a..8153803e30 100644
--- a/test/parallel/test-listen-fd-ebadf.js+++ b/test/parallel/test-listen-fd-ebadf.js@@ -1,11 +1,29 @@
'use strict';
const common = require('../common');
+
const assert = require('assert');
+const fs = require('fs');
const net = require('net');
net.createServer(common.mustNotCall()).listen({fd: 2})
.on('error', common.mustCall(onError));
+<<<<<<< HEAD
net.createServer(common.mustNotCall()).listen({fd: 42})
+||||||| parent of 1d8789188f... test: improve flaky test-listen-fd-ebadf.js+net.createServer(common.mustNotCall()).listen({ fd: 42 })+=======++let invalidFd = 2;++// Get first known bad file descriptor.+try {+ while (fs.fstatSync(++invalidFd));+} catch (e) {+ // do nothing; we now have an invalid fd+}++net.createServer(common.mustNotCall()).listen({ fd: invalidFd })+>>>>>>> 1d8789188f... test: improve flaky test-listen-fd-ebadf.js
.on('error', common.mustCall(onError));
function onError(ex) {

[Trott]

@gibfahn Merge conflict is caused by #14162 which added whitespace but hasn't yet been backported. Backport was requested in October so I guess it's not coming. That's unfortunate, because all those whitespace changes are likely to cause further merge conflicts. Oh well. At least it's easy to resolve: Remove the line from HEAD and keep all the lines from this PR. Done!

[Trott]

@gibfahn Backport in #18362.