event_pool.rb

Factory.define :event_pool do |p|
  p.name "Some event pool"
end

result

$: RAILS_ENV=test script/console

>> Factory(:user)

ActiveRecord::StatementInvalid: PGError: ERROR:  null value in column "user_id" violates not-null constraint
: INSERT INTO "event_pools" ("name", "created_at", "updated_at", "user_id") VALUES(E'Some event pool', '2009-11-05 15:39:34.361234', '2009-11-05 15:39:34.361234', NULL) RETURNING "id"

user.rb

Factory.define :user do |u|
  u.email 'user@example.com'
  u.password 'somepassword'
  u.password_confirmation 'somepassword'
  # u.association :event_pool
end

# factory_girl creates associations first, thus user_id is NULL (thanks jferris via #thoughtbot IRC)