unit test for not duplicating event listeners

Author: arturgawlik

test/parallel/test-net-socket-not-duplicates-destroy-soon-listeners.js

@@ -0,0 +1,14 @@
+'use strict';
+const assert = require('assert');
+const net = require('net');
+
+const socket = new net.Socket();
+socket.on('error', () => {});
+socket.connect({ host: 'non-existing.domain', port: 1234 });
+socket.destroySoon();
+socket.connect({ host: 'non-existing.domain', port: 1234 });
+socket.destroySoon();
+const finishListenersCount = socket.listeners('finish').length;
+const connectListenersCount = socket.listeners('connect').length;
+assert.equal(finishListenersCount, 1);
+assert.equal(connectListenersCount, 1);