test: check number of message events

When a no-op message event handler is used in a test, make it clear what
is expected by using `common.mustCall()` and `common.mustNotCall()`.
PR-URL: #13125
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <mhdawson@ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott

test/parallel/test-child-process-fork-ref2.js

@@ -1,5 +1,5 @@
 'use strict';
-require('../common');
+constcommon=require('../common');
 constfork=require('child_process').fork;
 
 if(process.argv[2]==='child'){
@@ -8,7 +8,7 @@ if (process.argv[2] === 'child') {
 
 setTimeout(function(){
 console.log('child -> will this keep it alive?');
-process.on('message',function(){});
+process.on('message',common.mustNotCall());
 },400);
 
 }else{

test/sequential/test-child-process-pass-fd.js

@@ -45,7 +45,7 @@ if (process.argv[2] !== 'child') {
 // the only thing keeping this worker alive will be IPC. This is important,
 // because it means a worker with no parent will have no referenced handles,
 // thus no work to do, and will exit immediately, preventing process leaks.
-process.on('message',common.noop);
+process.on('message',common.mustCall());
 
 constserver=net.createServer((c)=>{
 process.once('message',function(msg){