From 1d8789188fa156d5eb75c155f6c648c2bd96b842 Mon Sep 17 00:00:00 2001
From: Rich Trott <rtrott@gmail.com>
Date: Wed, 20 Dec 2017 13:59:14 -0800
Subject: [PATCH] test: improve flaky test-listen-fd-ebadf.js

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

PR-URL: https://github.com/nodejs/node/pull/17797
Fixes: https://github.com/nodejs/node/issues/17762
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
---
 test/parallel/test-listen-fd-ebadf.js | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/test/parallel/test-listen-fd-ebadf.js b/test/parallel/test-listen-fd-ebadf.js
index 0f09d386d5fa7c..564dea7f951a1a 100644
--- a/test/parallel/test-listen-fd-ebadf.js
+++ b/test/parallel/test-listen-fd-ebadf.js
@@ -21,12 +21,24 @@
 
 '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));
-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 })
   .on('error', common.mustCall(onError));
 
 function onError(ex) {