http2: add bytesWritten test for Http2Stream

note that this is for the `Http2Server` class. I'll soon be
adding one for `Http2SecureServer` as well.

Refs: #29829

PR-URL: #33162
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-http2-byteswritten-server.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+const assert = require('assert');
+const http2 = require('http2');
+
+const http2Server = http2.createServer(common.mustCall(function(req, res) {
+  res.socket.on('finish', common.mustCall(() => {
+    assert(req.socket.bytesWritten > 0); // 1094
+  }));
+  res.writeHead(200, { 'Content-Type': 'text/plain' });
+  res.write(Buffer.from('1'.repeat(1024)));
+  res.end();
+}));
+
+http2Server.listen(0, common.mustCall(function() {
+  const URL = `http://localhost:${http2Server.address().port}`;
+  const http2client = http2.connect(URL, { protocol: 'http:' });
+  const req = http2client.request({ ':method': 'GET', ':path': '/' });
+  req.on('data', common.mustCall());
+  req.on('end', common.mustCall(function() {
+    http2client.close();
+    http2Server.close();
+  }));
+  req.end();
+}));