NameError: uninitialized constant UserTest::Factory

Problem
You are trying to use shoulda with factory_girl but you are getting the above error:

NameError: uninitialized constant UserTest::Factory

Solution
Insert the following to your config/environments/test.rb
config.gem 'shoulda', :lib => 'shoulda'

install the gem with:
sudo gem install shoulda

add the following to your test/test_helper.rb
require 'factory_girl'
require "factories"

in your test use the new syntax without the underscore, as in:
should belong_to(:model)