test: fix another flaky stringbytes test

Avoid depending on precise timing of when an object will be collected
by GC. This test was missed by #6039 as it happened to be in a
different directory than the rest.

Ref: https://github.com/nodejs/node/pull/6039
PR-URL: https://github.com/nodejs/node/pull/6073
Reviewed-By: Trott - Rich Trott <rtrott@gmail.com>

test/README.md

@@ -10,7 +10,9 @@ Tests for when the `--abort-on-uncaught-exception` flag is used.
 
 ### addons
 
-Tests for [addon](https://nodejs.org/api/addons.html) functionality.
+Tests for [addon](https://nodejs.org/api/addons.html) functionality along with
+some tests that require an addon to function properly.
+
 
 | Runs on CI |
 |:----------:|

test/parallel/test-stringbytes-external-at-max.js → test/addons/stringbytes-external-exceed-max/test-stringbytes-external-at-max.js

@@ -1,7 +1,7 @@
 'use strict';
-// Flags: --expose-gc
 
-const common = require('../common');
+const common = require('../../common');
+const binding = require('./build/Release/binding');
 const assert = require('assert');
 
 // v8 fails silently if string length > v8::String::kMaxLength
@@ -14,13 +14,9 @@ if (!common.enoughTestMem) {
   console.log(skipMessage);
   return;
 }
-assert(typeof gc === 'function', 'Run this test with --expose-gc');
 
 try {
   var buf = Buffer.allocUnsafe(kStringMaxLength);
-  // Try to allocate memory first then force gc so future allocations succeed.
-  Buffer.allocUnsafe(2 * kStringMaxLength);
-  gc();
 } catch (e) {
   // If the exception is not due to memory confinement then rethrow it.
   if (e.message !== 'Array buffer allocation failed') throw (e);
@@ -28,5 +24,11 @@ try {
   return;
 }
 
+// Ensure we have enough memory available for future allocations to succeed.
+if (!binding.ensureAllocation(2 * kStringMaxLength)) {
+  console.log(skipMessage);
+  return;
+}
+
 const maxString = buf.toString('binary');
 assert.equal(maxString.length, kStringMaxLength);