test: duplicated buffer in test-stream2-writable.js

PR-URL: nodejs#28380
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Adrian Estrada <edsadr@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-stream2-writable.js

@@ -229,10 +229,12 @@ for (let i = 0; i < chunks.length; i++) {
   tw.end(common.mustCall());
 }
 
+const helloWorldBuffer = Buffer.from('hello world');
+
 {
   // Verify end() callback with chunk
   const tw = new TestWriter();
-  tw.end(Buffer.from('hello world'), common.mustCall());
+  tw.end(helloWorldBuffer, common.mustCall());
 }
 
 {
@@ -244,15 +246,15 @@ for (let i = 0; i < chunks.length; i++) {
 {
   // Verify end() callback after write() call
   const tw = new TestWriter();
-  tw.write(Buffer.from('hello world'));
+  tw.write(helloWorldBuffer);
   tw.end(common.mustCall());
 }
 
 {
   // Verify end() callback after write() callback
   const tw = new TestWriter();
   let writeCalledback = false;
-  tw.write(Buffer.from('hello world'), function() {
+  tw.write(helloWorldBuffer, function() {
     writeCalledback = true;
   });
   tw.end(common.mustCall(function() {