how to test engineio?

[ruandao]

appledeMacBook-Pro-2:websocket ruandao$ websocket-bench -g generator.js -t engine.io -a 100 -c 40 http://localhost:5000/engine.io/
Launch bench with 100 total connection, 40 concurent connection
0 message(s) send by client
1 worker(s)
WS server : engine.io
/usr/local/lib/node_modules/websocket-bench/lib/worker.js:36
var worker = new BenchmarkWorker(server, generator, verbose);
             ^

TypeError: BenchmarkWorker is not a function
    at Object.<anonymous> (/usr/local/lib/node_modules/websocket-bench/lib/worker.js:36:14)
    at Module._compile (module.js:413:34)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Function.Module.runMain (module.js:447:10)
    at startup (node.js:142:18)
    at node.js:939:3
events.js:154
      throw er; // Unhandled 'error' event
      ^

Error: channel closed
    at ChildProcess.target.send (internal/child_process.js:523:16)
    at Benchmark._nextStep (/usr/local/lib/node_modules/websocket-bench/lib/benchmark.js:87:21)
    at Timeout._onTimeout (/usr/local/lib/node_modules/websocket-bench/lib/benchmark.js:100:13)
    at tryOnTimeout (timers.js:224:11)
    at Timer.listOnTimeout (timers.js:198:5)