test: harden test-gc-http-client

This reduces the total number of requests from 500 to 300 and triggers
more requests in parallel. It also moves some function creation out
and waits with the first request until the server is listening.

Fixes: #22336

test/parallel/test-gc-http-client.js

@@ -10,44 +10,40 @@ function serverHandler(req, res) {
 }
 
 const http = require('http');
-const todo = 500;
+const todo = 300;
 let done = 0;
 let count = 0;
 let countGC = 0;
 
 console.log(`We should do ${todo} requests`);
 
 const server = http.createServer(serverHandler);
-server.listen(0, getall);
-
+server.listen(0, common.mustCall(() => {
+  for (let i = 0; i < 15; i++)
+    getall();
+}));
 
 function getall() {
-  if (count >= todo)
+  if (count === todo)
     return;
 
-  (function() {
-    function cb(res) {
-      res.resume();
-      console.error('in cb');
-      done += 1;
-      res.on('end', global.gc);
-    }
-
-    const req = http.get({
-      hostname: 'localhost',
-      pathname: '/',
-      port: server.address().port
-    }, cb);
+  const req = http.get({
+    hostname: 'localhost',
+    pathname: '/',
+    port: server.address().port
+  }, cb);
 
-    count++;
-    common.onGC(req, { ongc });
-  })();
+  count++;
+  common.onGC(req, { ongc });
 
   setImmediate(getall);
 }
 
-for (let i = 0; i < 10; i++)
-  getall();
+function cb(res) {
+  res.resume();
+  done += 1;
+  res.on('end', global.gc);
+}
 
 function ongc() {
   countGC++;