test: fix test-buffer-tostring-range on allocation failure

If the test cannot allocate a buffer over 4GB, there is no point
continue testing toString() on it.

This also split the test case to a different file for clarity and
reduce interference with other cases.

PR-URL: #58416
Fixes: #56726
Reviewed-By: LiviaMedeiros <livia@cirno.name>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
Reviewed-By: Stefan Stojanovic <stefan.stojanovic@janeasystems.com>

Author: joyeecheung

test/parallel/test-buffer-tostring-4gb.js

@@ -0,0 +1,20 @@
+'use strict';
+
+// This tests that Buffer.prototype.toString() works with buffers over 4GB.
+const common = require('../common');
+
+// Must not throw when start and end are within kMaxLength
+// Cannot test on 32bit machine as we are testing the case
+// when start and end are above the threshold
+common.skipIf32Bits();
+const threshold = 0xFFFFFFFF; // 2^32 - 1
+let largeBuffer;
+try {
+  largeBuffer = Buffer.alloc(threshold + 20);
+} catch (e) {
+  if (e.code === 'ERR_MEMORY_ALLOCATION_FAILED' || /Array buffer allocation failed/.test(e.message)) {
+    common.skip('insufficient space for Buffer.alloc');
+  }
+  throw e;
+}
+largeBuffer.toString('utf8', threshold, threshold + 20);

test/parallel/test-buffer-tostring-range.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 
 const rangeBuffer = Buffer.from('abc');
@@ -98,11 +98,3 @@ assert.throws(() => {
   name: 'TypeError',
   message: 'Unknown encoding: null'
 });
-
-// Must not throw when start and end are within kMaxLength
-// Cannot test on 32bit machine as we are testing the case
-// when start and end are above the threshold
-common.skipIf32Bits();
-const threshold = 0xFFFFFFFF;
-const largeBuffer = Buffer.alloc(threshold + 20);
-largeBuffer.toString('utf8', threshold, threshold + 20);