Test::Unit test for unique property in Rails

gistfile1.rb

# Test in test/functional/sites_controller_test.rb
test "should be unique" do
  link1 = sites(:one)
  link1.save
  link2 = Site.new(sites(:two))
  link2.url = link1.url
  assert !link2.save, "Saved a link with the same url"
end

# Implementation in app/model/site.rb
class Site < ActiveRecord::Base
  validates_uniqueness_of :url
end