user-steps.rb

var User = require('../../models/user');

module.exports = function(){
  this.World = require('../support/world').World;

  this.When(/^I go to create a new user$/, function(next) {
    this.visit('/users/new', next);
  });

  this.When(/^I enter "([^"]*)" as the "([^"]*)"$/, function(value, field, next) {
    this.browser.fill(field, value, next);
  });

  this.When(/^I click "([^"]*)"$/, function(button, callback) {
    this.browser.pressButton(button, callback);
  });
};

users.feature

  Scenario: Create a new user
    Given I am an administrator
    When I go to create a new user
    And I enter "peter" as the "Username"
    And I enter "[email protected]" as the "Email"
    And I click "Submit"
    Then I should see "peter"
    And I should see "[email protected]

world.js

  var zombie = require('zombie')
  , HTML5  = require('html5')
  , should = require('should')
  , server = require('../../app')
  , databaseCleaner = require('database-cleaner')
  , dbCleaner = new DatabaseCleaner('mongodb');

exports.World = function MyWorld(callback){
  this.browser = new zombie.Browser({runScripts:true, debug:false, htmlParser: HTML5});
 
  this.page = function(path){
   return "http://localhost:" + server.address().port + path
  };

  this.visit = function(path, callback){
    this.browser.visit( this.page(path), function(err, browser, status){
      callback(err, browser, status);
    });
  };

  this.clean = function(callback){
     dbCleaner.clean(mongoose.connection.db, callback);
  }

  callback(this);
};

You should export World with exports.World = instead of module.exports = as you are requiring it through the World property of the module in your step definitions.

i adjusted it as above, but same problem though.

TypeError: undefined is not a function at CALL_NON_FUNCTION (native) at new MyWorld (/Users/jay/github/tilt/features/support/world.js:25:3) at Object.instantiateNewWorld (/Users/jay/.nvm/v0.4.7/lib/node_modules/cucumber/lib/cucumber/support_code/library.js:30:14)