title: FactoryGirl - override association with trait?
body: <p>Let's say I have the following <code>ActiveRecord</code> models:</p>
  
  <pre><code>class Car
    belongs_to :driver
  end
  
  class Driver
    # Has attribute :name
    has_one :car
  end
  </code></pre>
  
  <p>And I define a couple of factories using these models:</p>
  
  <pre><code>FactoryGirl.define do
    factory :car do
      association :driver
  
      trait :fast_car do
        association :driver, :fast
      end
    end
  end
  
  FactoryGirl.define do
    factory :driver do
      name 'Jason'
  
      trait :fast do
        name 'Mario'
      end
    end
  end
  </code></pre>
  
  <p>When I execute the following code:</p>
  
  <pre><code>car = FactoryGirl.create(:car, :fast_car)
  </code></pre>
  
  <p>I would expect <code>car.driver.name</code> to equal <code>Mario</code>, but instead it equals <code>Jason</code>. This leads me to believe that you can't use traits to override associations for factories. Is this true? If so, what would be the proper way to override the associated <code>Driver</code> for a fast car?</p>