test: refactor the code in test-http-keep-alive

* use common.mustCall to control the functions execution automatically
* use let and const instead of var
* use assert.strictEqual instead assert.equal
PR-URL: #10350
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>

Author: edsadr

test/parallel/test-http-keep-alive.js

@@ -1,51 +1,51 @@
 'use strict';
-require('../common');
-varassert=require('assert');
-varhttp=require('http');
+constcommon=require('../common');
+constassert=require('assert');
+consthttp=require('http');
 
-varbody='hello world\n';
+constserver=http.createServer(common.mustCall((req,res)=>{
+constbody='hello world\n';
 
-varserver=http.createServer(function(req,res){
 res.writeHead(200,{'Content-Length': body.length});
 res.write(body);
 res.end();
-});
+},3));
 
-varagent=newhttp.Agent({maxSockets: 1});
-varheaders={'connection': 'keep-alive'};
-varname;
+constagent=newhttp.Agent({maxSockets: 1});
+constheaders={'connection': 'keep-alive'};
+letname;
 
-server.listen(0,function(){
+server.listen(0,common.mustCall(function(){
 name=agent.getName({port: this.address().port});
 http.get({
 path: '/',headers: headers,port: this.address().port,agent: agent
-},function(response){
-assert.equal(agent.sockets[name].length,1);
-assert.equal(agent.requests[name].length,2);
+},common.mustCall((response)=>{
+assert.strictEqual(agent.sockets[name].length,1);
+assert.strictEqual(agent.requests[name].length,2);
 response.resume();
-});
+}));
 
 http.get({
 path: '/',headers: headers,port: this.address().port,agent: agent
-},function(response){
-assert.equal(agent.sockets[name].length,1);
-assert.equal(agent.requests[name].length,1);
+},common.mustCall((response)=>{
+assert.strictEqual(agent.sockets[name].length,1);
+assert.strictEqual(agent.requests[name].length,1);
 response.resume();
-});
+}));
 
 http.get({
 path: '/',headers: headers,port: this.address().port,agent: agent
-},function(response){
-response.on('end',function(){
-assert.equal(agent.sockets[name].length,1);
+},common.mustCall((response)=>{
+response.on('end',common.mustCall(()=>{
+assert.strictEqual(agent.sockets[name].length,1);
 assert(!agent.requests.hasOwnProperty(name));
 server.close();
-});
+}));
 response.resume();
-});
-});
+}));
+}));
 
-process.on('exit',function(){
+process.on('exit',()=>{
 assert(!agent.sockets.hasOwnProperty(name));
 assert(!agent.requests.hasOwnProperty(name));
 });