cocktails.rb

FactoryGirl.define do
  factory :cocktail do
    name "Desert Healer"
    user
    photo Rack::Test::UploadedFile.new(File.open(Rails.root.join("spec/fixtures/files/deserthealer.jpg")))
    ingredients { build_list(:ingredient, 1) }
  end
end

ingredients.rb

FactoryGirl.define do
  factory :ingredient do
    name "Bourbon"
    quantity 1
    unit "oz"

    after(:build) do |i|
      i.cocktail = build(:cocktail, ingredients: [i]) unless i.cocktail
    end
  end
end