add simple unittest

test/broadcast-server.js

@@ -0,0 +1,23 @@
+const WebSocket = require('ws');
+
+const wss = new WebSocket.Server({ port: 8080 });
+
+// Broadcast to all.
+wss.broadcast = function broadcast(data) {
+  wss.clients.forEach(function each(client) {
+    if (client.readyState === WebSocket.OPEN) {
+      client.send(data);
+    }
+  });
+};
+
+wss.on('connection', function connection(ws) {
+  ws.on('message', function incoming(data) {
+    // Broadcast to everyone else.
+    wss.clients.forEach(function each(client) {
+      if (client !== ws && client.readyState === WebSocket.OPEN) {
+        client.send(data);
+      }
+    });
+  });
+});