test: use countdown timer

PR-URL: nodejs#17326
Refs: nodejs#17169
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-http-response-status-message.js

@@ -24,8 +24,7 @@ require('../common');
 const assert = require('assert');
 const http = require('http');
 const net = require('net');
-
-let testsComplete = 0;
+const Countdown = require('../common/countdown');
 
 const testCases = [
   { path: '/200', statusMessage: 'OK',
@@ -59,6 +58,8 @@ const server = net.createServer(function(connection) {
   });
 });
 
+const countdown = new Countdown(testCases.length, () => server.close());
+
 function runTest(testCaseIndex) {
   const testCase = testCases[testCaseIndex];
 
@@ -71,12 +72,9 @@ function runTest(testCaseIndex) {
     assert.strictEqual(testCase.statusMessage, response.statusMessage);
 
     response.on('end', function() {
-      testsComplete++;
-
+      countdown.dec();
       if (testCaseIndex + 1 < testCases.length) {
         runTest(testCaseIndex + 1);
-      } else {
-        server.close();
       }
     });
 
@@ -85,7 +83,3 @@ function runTest(testCaseIndex) {
 }
 
 server.listen(0, function() { runTest(0); });
-
-process.on('exit', function() {
-  assert.strictEqual(testCases.length, testsComplete);
-});