test: make test-http2-buffersize more correct

Previously, this code could have closed the server before the
connection was actually received by the server, as the `'close'`
event on the client side can be emitted before the connection
is established.
The following commit exacerbates this problem, so fix the test first.
PR-URL: #31502
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

Author: addaleax

test/parallel/test-http2-buffersize.js

@@ -15,29 +15,32 @@ const Countdown = require('../common/countdown');
 constBUFFER_SIZE=30;
 constserver=createServer();
 
+letclient;
+constcountdown=newCountdown(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)=>{
 stream.on('data',mustCall());
 stream.on('end',mustCall());
+
+stream.on('close',mustCall(()=>{
+countdown.dec();
+}));
 },SOCKETS));
 
 server.listen(0,mustCall(()=>{
 constauthority=`http://localhost:${server.address().port}`;
-constclient=connect(authority);
-constcountdown=newCountdown(SOCKETS,()=>{
-client.close();
-server.close();
-});
+client=connect(authority);
 
 client.once('connect',mustCall());
 
 for(letj=0;j<SOCKETS;j+=1){
 conststream=client.request({':method': 'POST'});
 stream.on('data',()=>{});
-stream.on('close',mustCall(()=>{
-countdown.dec();
-}));
 
 for(leti=0;i<TIMES;i+=1){
 stream.write(Buffer.allocUnsafe(BUFFER_SIZE),mustCall());