test: refactor test-net-keepalive.js

- Replace require() vars with const.
- Replace assert.equal() with assert.strictEqual().
- Add common.mustCall() to the setTimeout() callback.
PR-URL: #9995
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: kmccmk9

test/parallel/test-net-keepalive.js

@@ -1,20 +1,20 @@
 'use strict';
-varcommon=require('../common');
-varassert=require('assert');
-varnet=require('net');
+constcommon=require('../common');
+constassert=require('assert');
+constnet=require('net');
 
 varserverConnection;
 varclientConnection;
 varechoServer=net.createServer(function(connection){
 serverConnection=connection;
-setTimeout(function(){
+setTimeout(common.mustCall(function(){
 // make sure both connections are still open
-assert.equal(serverConnection.readyState,'open');
-assert.equal(clientConnection.readyState,'open');
+assert.strictEqual(serverConnection.readyState,'open');
+assert.strictEqual(clientConnection.readyState,'open');
 serverConnection.end();
 clientConnection.end();
 echoServer.close();
-},common.platformTimeout(100));
+},1),common.platformTimeout(100));
 connection.setTimeout(0);
 assert.notEqual(connection.setKeepAlive,undefined);
 // send a keepalive packet after 50 ms