events: add unique events benchmark

Co-authored-by: Brian White <mscdex@mscdex.net>
PR-URL: https://github.com/nodejs/node/pull/44657
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

benchmark/events/ee-listen-unique.js

@@ -0,0 +1,35 @@
+'use strict';
+const common = require('../common.js');
+const { EventEmitter } = require('events');
+
+const bench = common.createBenchmark(main, {
+  events: [1, 2, 3, 5, 10, 20],
+  n: [1e6],
+});
+
+function main({ events, n }) {
+  const ee = new EventEmitter();
+  const listeners = [];
+
+  for (let k = 0; k < 10; k += 1)
+    listeners.push(() => {});
+
+  const eventNames = [];
+  for (let k = 0; k < events; ++k)
+    eventNames.push(`dummy${k}`);
+
+  bench.start();
+  for (let i = 0; i < n; i += 1) {
+    for (const eventName of eventNames) {
+      for (let k = listeners.length; --k >= 0; /* empty */) {
+        ee.on(eventName, listeners[k]);
+      }
+    }
+    for (const eventName of eventNames) {
+      for (let k = listeners.length; --k >= 0; /* empty */) {
+        ee.removeListener(eventName, listeners[k]);
+      }
+    }
+  }
+  bench.end(n);
+}