person_spec.rb

  # person.rb

    validates_presence_of :address

  # person_factory.rb

    Factory.define :person do |p|
      p.name   'John'
      p.surname 'Doe'
      p.association :address
    end

  # person_spec.rb

  it "builds a valid person with factory girl" do
    Factory.build(:person).should be_valid
  end