test: refactor test-pipe-file-to-http

Changing var defs to const/let, changing assert.equal to
assert.strictEqual. Wrapping functions called once with
common.mustCall

PR-URL: https://github.com/nodejs/node/pull/10054
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-pipe-file-to-http.js

@@ -1,20 +1,19 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
-var fs = require('fs');
-var http = require('http');
-var path = require('path');
-var cp = require('child_process');
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const http = require('http');
+const path = require('path');
+const cp = require('child_process');
 
 common.refreshTmpDir();
 
-var filename = path.join(common.tmpDir || '/tmp', 'big');
-var clientReqComplete = false;
-var count = 0;
+const filename = path.join(common.tmpDir || '/tmp', 'big');
+let count = 0;
 
-var server = http.createServer(function(req, res) {
-  var timeoutId;
-  assert.equal('POST', req.method);
+const server = http.createServer(function(req, res) {
+  let timeoutId;
+  assert.strictEqual('POST', req.method);
   req.pause();
 
   setTimeout(function() {
@@ -36,27 +35,26 @@ var server = http.createServer(function(req, res) {
 server.listen(0);
 
 server.on('listening', function() {
-  var cmd = common.ddCommand(filename, 10240);
+  const cmd = common.ddCommand(filename, 10240);
 
-  cp.exec(cmd, function(err, stdout, stderr) {
+  cp.exec(cmd, function(err) {
     if (err) throw err;
     makeRequest();
   });
 });
 
 function makeRequest() {
-  var req = http.request({
+  const req = http.request({
     port: server.address().port,
     path: '/',
     method: 'POST'
   });
 
-  var s = fs.ReadStream(filename);
+  const s = fs.ReadStream(filename);
   s.pipe(req);
-  s.on('close', function(err) {
-    if (err) throw err;
-    clientReqComplete = true;
-  });
+  s.on('close', common.mustCall((err) => {
+    assert.ifError(err);
+  }));
 
   req.on('response', function(res) {
     res.resume();
@@ -67,6 +65,5 @@ function makeRequest() {
 }
 
 process.on('exit', function() {
-  assert.equal(1024 * 10240, count);
-  assert.ok(clientReqComplete);
+  assert.strictEqual(1024 * 10240, count);
 });