use_instantiated_fixtures and use_transactional_fixtures defaults are set in active_record/fixtures

railties/lib/rails/test_help.rb

@@ -9,8 +9,6 @@
   class ActiveSupport::TestCase
     include ActiveRecord::TestFixtures
     self.fixture_path = "#{Rails.root}/test/fixtures/"
-    self.use_instantiated_fixtures  = false
-    self.use_transactional_fixtures = true
   end
 
   ActionController::IntegrationTest.fixture_path = ActiveSupport::TestCase.fixture_path