factories.rb

require 'factory_girl'

FactoryGirl.define do
  factory :user do
    name 'Pete'
  end

  factory :registration do
    title 'Summer Class'
  end
  
  factory :user_registration do
    user
    registration
  end
end

user_registration_spec.rb

require 'spec_helper'

describe "Connecting Users to Registrations through 2 Factories" do
  before :each do
    @user = create(:user)
    @registration = create(:registration)
    @user.registrations << @registration
  end

  it "should associate the user with the registration" do
    expect(@user.name).to eq 'Pete'
    expect(@registration.title).to eq 'Summer Class'
    expect(@user.registrations.length).to eq 1
  end
  
  describe "Connecting Users to Registrations through 1 Factory" do
    before :each do
      @user_and_registration = create(:user_registration)
    end
    
    it "should create a new user and new registration and associate them" do
      expect(@user_and_registration.user.name).to eq 'Pete'
      expect(@user_and_registration.registration.title).to eq 'Summer Class'
    end
  end
end