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

Find an invalid file descriptor rather than assuming 42 will be invalid. PR-URL: #17797 Fixes: #17762 Reviewed-By: Gibson Fahnestock <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Khaidi Chu <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: Ruben Bridgewater <[email protected]>
nodejs · Feb 5, 2018 · b6a2b6e · b6a2b6e
1 parent 75fbd51
commit b6a2b6e
Showing 1 changed file with 13 additions and 1 deletion.
diff --git a/test/parallel/test-listen-fd-ebadf.js b/test/parallel/test-listen-fd-ebadf.js
@@ -1,11 +1,23 @@
 '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) {