test: change var declarations, add mustCall check

In this test, I changed the var declarations to be either a let or a
const. For some of the callbacks, I added a mustCall check to ensure
that the functions have run. I also changed assert.equal() to
assert.strictEqual().
PR-URL: #9962
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: Daniel Sims

test/parallel/test-cluster-net-send.js

@@ -1,50 +1,51 @@
 'use strict';
-varcommon=require('../common');
-varassert=require('assert');
-varfork=require('child_process').fork;
-varnet=require('net');
+constcommon=require('../common');
+constassert=require('assert');
+constfork=require('child_process').fork;
+constnet=require('net');
 
 if(process.argv[2]!=='child'){
 console.error('[%d] master',process.pid);
 
-varworker=fork(__filename,['child']);
-varcalled=false;
+constworker=fork(__filename,['child']);
+letcalled=false;
 
-worker.once('message',function(msg,handle){
-assert.equal(msg,'handle');
+worker.once('message',common.mustCall(function(msg,handle){
+assert.strictEqual(msg,'handle');
 assert.ok(handle);
 worker.send('got');
 
 handle.on('data',function(data){
 called=true;
-assert.equal(data.toString(),'hello');
+assert.strictEqual(data.toString(),'hello');
 });
 
 handle.on('end',function(){
 worker.kill();
 });
-});
+}));
 
 process.once('exit',function(){
 assert.ok(called);
 });
 }else{
 console.error('[%d] worker',process.pid);
 
-varsocket;
-varcbcalls=0;
+letsocket;
+letcbcalls=0;
 functionsocketConnected(){
 if(++cbcalls===2)
 process.send('handle',socket);
 }
 
-varserver=net.createServer(function(c){
-process.once('message',function(msg){
-assert.equal(msg,'got');
+constserver=net.createServer(function(c){
+process.once('message',common.mustCall(function(msg){
+assert.strictEqual(msg,'got');
 c.end('hello');
-});
+}));
 socketConnected();
 });
+
 server.listen(common.PORT,function(){
 socket=net.connect(common.PORT,'127.0.0.1',socketConnected);
 });