test: refactor test-http2-buffersize

Remove seemlingly misplaced and/or extraneous comment. Replace countdown
with Promise.all.

PR-URL: #32540
Reviewed-By: Anna Henningsen <anna@addaleax.net>

test/parallel/test-http2-buffersize.js

@@ -5,46 +5,45 @@ if (!hasCrypto)
   skip('missing crypto');
 const assert = require('assert');
 const { createServer, connect } = require('http2');
-const Countdown = require('../common/countdown');
+const { once } = require('events');
 
 // This test ensures that `bufferSize` of Http2Session and Http2Stream work
 // as expected.
 {
-  const SOCKETS = 2;
-  const TIMES = 10;
-  const BUFFER_SIZE = 30;
+  const kSockets = 2;
+  const kTimes = 10;
+  const kBufferSize = 30;
   const server = createServer();
 
   let client;
-  const countdown = new Countdown(SOCKETS, () => {
-    client.close();
-    server.close();
-  });
 
-  // Other `bufferSize` tests for net module and tls module
-  // don't assert `bufferSize` of server-side sockets.
-  server.on('stream', mustCall((stream) => {
+  const getStream = async () => {
+    const [ stream ] = await once(server, 'stream');
     stream.on('data', mustCall());
     stream.on('end', mustCall());
+    stream.on('close', mustCall());
+    return once(stream, 'close');
+  };
 
-    stream.on('close', mustCall(() => {
-      countdown.dec();
-    }));
-  }, SOCKETS));
+  const promises = [...new Array(kSockets)].map(getStream);
+  Promise.all(promises).then(mustCall(() => {
+    client.close();
+    server.close();
+  }));
 
   server.listen(0, mustCall(() => {
     const authority = `http://localhost:${server.address().port}`;
     client = connect(authority);
 
     client.once('connect', mustCall());
 
-    for (let j = 0; j < SOCKETS; j += 1) {
+    for (let j = 0; j < kSockets; j += 1) {
       const stream = client.request({ ':method': 'POST' });
       stream.on('data', () => {});
 
-      for (let i = 0; i < TIMES; i += 1) {
-        stream.write(Buffer.allocUnsafe(BUFFER_SIZE), mustCall());
-        const expectedSocketBufferSize = BUFFER_SIZE * (i + 1);
+      for (let i = 0; i < kTimes; i += 1) {
+        stream.write(Buffer.allocUnsafe(kBufferSize), mustCall());
+        const expectedSocketBufferSize = kBufferSize * (i + 1);
         assert.strictEqual(stream.bufferSize, expectedSocketBufferSize);
       }
       stream.end();