test: refactor test-stdin-script-child

- var -> const where possible
- assert.equal -> assert.strictEqual
- passed the setTimeout function a second parameter for readability
- used assert.strictEqual for assert(!c) as it is expected to be 0 and
not some other value
PR-URL: #10321
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>

Author: emanuelbuholzer

test/parallel/test-stdin-script-child.js

@@ -1,14 +1,14 @@
 'use strict';
-require('../common');
-varassert=require('assert');
+constcommon=require('../common');
+constassert=require('assert');
 
-varspawn=require('child_process').spawn;
-varchild=spawn(process.execPath,[],{
+constspawn=require('child_process').spawn;
+constchild=spawn(process.execPath,[],{
 env: Object.assign(process.env,{
 NODE_DEBUG: process.argv[2]
 })
 });
-varwanted=child.pid+'\n';
+constwanted=child.pid+'\n';
 varfound='';
 
 child.stdout.setEncoding('utf8');
@@ -21,12 +21,12 @@ child.stderr.on('data', function(c) {
 console.error('> '+c.trim().split(/\n/).join('\n> '));
 });
 
-child.on('close',function(c){
-assert(!c);
-assert.equal(found,wanted);
+child.on('close',common.mustCall(function(c){
+assert.strictEqual(c,0);
+assert.strictEqual(found,wanted);
 console.log('ok');
-});
+}));
 
 setTimeout(function(){
 child.stdin.end('console.log(process.pid)');
-});
+},1);