title: FactoryGirl: Creating dynamic factories with parameters?
body: <p>I have three factories that i  want to DRY up. They look like this:</p>
  
  <pre><code>factory :sequenced_stamps_by_years, class: Stamp do
    ...
    sequence(:day_date) { |n| n.years.ago }
  end
  
  factory :sequenced_stamps_by_months, class: Stamp do
    ...
    sequence(:day_date) { |n| n.months.ago }
  end
  
  factory :sequenced_stamps_by_weeks, class: Stamp do
    ...
    sequence(:day_date) { |n| n.weeks.ago }
  end
  </code></pre>
  
  <p>How can i dry this up? I want to be able to create them something like this:</p>
  
  <pre><code>FactoryGirl.create_list(:sequenced_stamps_by_x, 4, x: "weeks") ## &lt;- So that i can decide whether I want weeks, days, years, or months ago.
  </code></pre>
  
  <p>Is this possible?</p>