test: spawn new processes in vm-cached-data

V8 may start caching scripts from the first run soon. Preventively
execute scripts in another process to ensure no test failures due to
an update in the future.

See: #6258
PR-URL: #6280
Reviewed-By: Jochen Eisinger <jochen@chromium.org>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-vm-cached-data.js

@@ -2,19 +2,38 @@
 require('../common');
 const assert = require('assert');
 const vm = require('vm');
+const spawnSync = require('child_process').spawnSync;
 const Buffer = require('buffer').Buffer;
 
 function getSource(tag) {
  return `(function ${tag}() { return \'${tag}\'; })`;
 }
 
-function produce(source) {
- const script = new vm.Script(source, {
- produceCachedData: true
- });
- assert(!script.cachedDataProduced || script.cachedData instanceof Buffer);
+function produce(source, count) {
+ if (!count)
+ count = 1;
+
+ const out = spawnSync(process.execPath, [ '-e', `
+ var assert = require('assert');
+ var vm = require('vm');
+
+ let data;
+ for (var i = 0; i < ${count}; i++) {
+ var script = new vm.Script(process.argv[1], {
+ produceCachedData: true
+ });
+
+ assert(!script.cachedDataProduced || script.cachedData instanceof Buffer);
+
+ if (script.cachedDataProduced)
+ data = script.cachedData.toString('base64');
+ }
+ console.log(data);
+ `, source]);
+
+ assert.equal(out.status, 0, out.stderr + '');
 
- return script.cachedData;
+ return Buffer.from(out.stdout.toString(), 'base64');
 }
 
 function testProduceConsume() {
@@ -34,9 +53,7 @@ testProduceConsume();
 function testProduceMultiple() {
  const source = getSource('original');
 
- produce(source);
- produce(source);
- produce(source);
+ produce(source, 3);
 }
 testProduceMultiple();