test: move getTTYfd() to common helpers

This utility is fairly generic and likely useful for more than one test.

PR-URL: https://github.com/nodejs/node/pull/18800
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

2 files changed, 23 insertions, 0 deletions

diff --git a/test/common/README.md b/test/common/README.md
index e0a66e9da0..7fd36f5985 100644
--- a/test/common/README.md
+++ b/test/common/README.md
@@ -679,6 +679,12 @@ The realpath of the testing temporary directory.
 
 Deletes and recreates the testing temporary directory.
 
+### getTTYfd()
+
+Attempts to get a valid TTY file descriptor. Returns `-1` if it fails.
+
+The TTY file descriptor is assumed to be capable of being writable.
+
 ## WPT Module
 
 The wpt.js module is a port of parts of
diff --git a/test/common/index.js b/test/common/index.js
index b24d2158e7..1fc029292a 100644
--- a/test/common/index.js
+++ b/test/common/index.js
@@ -775,6 +775,23 @@ exports.crashOnUnhandledRejection = function() {
              (err) => process.nextTick(() => { throw err; }));
 };
 
+exports.getTTYfd = function getTTYfd() {
+  // Do our best to grab a tty fd.
+  const tty = require('tty');
+  // Don't attempt fd 0 as it is not writable on Windows.
+  // Ref: ef2861961c3d9e9ed6972e1e84d969683b25cf95
+  const ttyFd = [1, 2, 4, 5].find(tty.isatty);
+  if (ttyFd === undefined) {
+    try {
+      return fs.openSync('/dev/tty');
+    } catch (e) {
+      // There aren't any tty fd's available to use.
+      return -1;
+    }
+  }
+  return ttyFd;
+};
+
 // Hijack stdout and stderr
 const stdWrite = {};
 function hijackStdWritable(name, listener) {