test: give more time to GC in test-shadow-realm-gc-*

When --node-builtin-modules-path is used, we read and create
new strings for builtins in each realm which increases the memory
usage. As a result GC may not be able to keep up with the
allocation done in the loop in the test.

As a workaround, give GC a bit more time by waiting for a timer
in the loop.

test/common/gc.js

@@ -1,5 +1,7 @@
 'use strict';
 
+const wait = require('timers/promises').setTimeout;
+
 // TODO(joyeecheung): merge ongc.js and gcUntil from common/index.js
 // into this.
 
@@ -65,6 +67,15 @@ async function checkIfCollectable(
   createObject();
 }
 
+// Repeat an operation and give GC some breathing room at every iteration.
+async function runAndBreathe(fn, repeat, waitTime = 20) {
+  for (let i = 0; i < repeat; i++) {
+    await fn();
+    await wait(waitTime);
+  }
+}
+
 module.exports = {
   checkIfCollectable,
+  runAndBreathe,
 };

test/parallel/test-shadow-realm-gc-module.js

@@ -8,13 +8,11 @@
 
 const common = require('../common');
 const fixtures = require('../common/fixtures');
+const { runAndBreathe } = require('../common/gc');
 
-async function main() {
-  const mod = fixtures.fileURL('es-module-shadow-realm', 'state-counter.mjs');
-  for (let i = 0; i < 100; i++) {
-    const realm = new ShadowRealm();
-    await realm.importValue(mod, 'getCounter');
-  }
-}
+const mod = fixtures.fileURL('es-module-shadow-realm', 'state-counter.mjs');
 
-main().then(common.mustCall());
+runAndBreathe(async () => {
+  const realm = new ShadowRealm();
+  await realm.importValue(mod, 'getCounter');
+}, 100).then(common.mustCall());

test/parallel/test-shadow-realm-gc.js

@@ -6,14 +6,16 @@
  */
 
 const common = require('../common');
+const { runAndBreathe } = require('../common/gc');
 const assert = require('assert');
 const { isMainThread, Worker } = require('worker_threads');
 
-for (let i = 0; i < 100; i++) {
+runAndBreathe(() => {
   const realm = new ShadowRealm();
   realm.evaluate('new TextEncoder(); 1;');
-}
+}, 100).then(common.mustCall());
 
+// Test it in worker too.
 if (isMainThread) {
   const worker = new Worker(__filename);
   worker.on('exit', common.mustCall((code) => {