How do I test this?

subject.js

module.exports = function(input, output, cb) {
  input.on('data', function(chunk) {
    // do somethink with chunk, possibly transform it
    output.write(chunk);
  });

  input.on('end', function() {
    cb();
  });
};

test.js

var Readable = require('stream').Readable;
var Writable = require('stream').Writable;
var test = require('tape');
var subject = require('./subject');

test('it writes input to output stream', function(t) {
  var result = '';
  var input = new Readable();
  var output = new Writable();

  subject(input, output, function() {
    t.equal(result, 'I have no idea what I am doing.');
    t.end();
  });
});