node/test/simple/test-stream-pipe-event.js

var stream = require('stream');
var assert = require('assert');
var util = require('util');

function Writable () {
  this.writable = true;
  stream.Stream.call(this);
}
util.inherits(Writable, stream.Stream);

function Readable () {
  this.readable = true;
  stream.Stream.call(this);
}
util.inherits(Readable, stream.Stream);

var passed = false;

var w = new Writable();
w.on('pipe', function (src) {
  passed = true;
});

var r = new Readable();
r.pipe(w);

assert.ok(passed)