test: use Promise.all() in test-hash-seed

We have several tests where a number of asynchronous processes need to
finish before some checks happen. These are done in a number of ways,
including (as here) using our Countdown testing module. I think
Promise.all() may be the idiomatic and ergonomic way to go for a lot of
these tests. Using this one to get feedback on the idea.
PR-URL: #32273
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

Author: Trott

test/pummel/test-hash-seed.js

@@ -1,31 +1,26 @@
 'use strict';
 
 // Check that spawn child doesn't create duplicated entries
-require('../common');
-constCountdown=require('../common/countdown');
-constREPETITIONS=2;
+constcommon=require('../common');
+constkRepetitions=2;
 constassert=require('assert');
 constfixtures=require('../common/fixtures');
-const{ spawn }=require('child_process');
+const{ promisify, debuglog }=require('util');
+constdebug=debuglog('test');
+
+const{ execFile }=require('child_process');
+constexecFilePromise=promisify(execFile);
 consttargetScript=fixtures.path('guess-hash-seed.js');
-constseeds=[];
 
-constrequiredCallback=()=>{
-console.log(`Seeds: ${seeds}`);
+constrequiredCallback=common.mustCall((results)=>{
+constseeds=results.map((val)=>val.stdout.trim());
+debug(`Seeds: ${seeds}`);
 assert.strictEqual(newSet(seeds).size,seeds.length);
-assert.strictEqual(seeds.length,REPETITIONS);
-};
-
-constcountdown=newCountdown(REPETITIONS,requiredCallback);
+assert.strictEqual(seeds.length,kRepetitions);
+});
 
-for(leti=0;i<REPETITIONS;++i){
-letresult='';
-constsubprocess=spawn(process.execPath,[targetScript]);
-subprocess.stdout.setEncoding('utf8');
-subprocess.stdout.on('data',(data)=>{result+=data;});
+constgenerateSeed=()=>execFilePromise(process.execPath,[targetScript]);
+constsubprocesses=[...newArray(kRepetitions)].map(generateSeed);
 
-subprocess.on('exit',()=>{
-seeds.push(result.trim());
-countdown.dec();
-});
-}
+Promise.all(subprocesses)
+.then(requiredCallback);