Problem with test file for latest ruby on rails

I downloaded the latest rails from the website and it gives the following test file:

require 'test_helper'

class ArticleTest < ActiveSupport::TestCase   # Replace this with your real tests.   def test_truth     assert true   end end

that is it!

Now when I run the above I get the error message:

C:\ruby\econstructor>ruby test\unit\article_test.rb c:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require': no such file to load -- test_helper (LoadError)         from c:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'         from test/unit/article_test.rb:1