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