test: use countdown in test file

Fixes: #17169

test/parallel/test-http-get-pipeline-problem.js

@@ -28,6 +28,7 @@ const fixtures = require('../common/fixtures');
 const assert = require('assert');
 const http = require('http');
 const fs = require('fs');
+const Countdown = require('../common/countdown');
 
 http.globalAgent.maxSockets = 1;
 
@@ -38,14 +39,12 @@ const image = fixtures.readSync('/person.jpg');
 console.log(`image.length = ${image.length}`);
 
 const total = 10;
-let requests = 0;
-let responses = 0;
+const responseCountdown = new Countdown(total, common.mustCall(() => {
+  checkFiles();
+  server.close();
+}));
 
 const server = http.Server(function(req, res) {
-  if (++requests === total) {
-    server.close();
-  }
-
   setTimeout(function() {
     res.writeHead(200, {
       'content-type': 'image/jpeg',
@@ -74,9 +73,7 @@ server.listen(0, function() {
 
         s.on('finish', function() {
           console.error(`done ${x}`);
-          if (++responses === total) {
-            checkFiles();
-          }
+          responseCountdown.dec();
         });
       }).on('error', function(e) {
         console.error('error! ', e.message);
@@ -86,8 +83,6 @@ server.listen(0, function() {
   }
 });
 
-
-let checkedFiles = false;
 function checkFiles() {
   // Should see 1.jpg, 2.jpg, ..., 100.jpg in tmpDir
   const files = fs.readdirSync(common.tmpDir);
@@ -101,13 +96,4 @@ function checkFiles() {
       image.length, stat.size,
       `size doesn't match on '${fn}'. Got ${stat.size} bytes`);
   }
-
-  checkedFiles = true;
 }
-
-
-process.on('exit', function() {
-  assert.strictEqual(total, requests);
-  assert.strictEqual(total, responses);
-  assert.ok(checkedFiles);
-});