Fix admin user factory

To avoid persistence and validation issues has_many associations
must be added after creation.

core/lib/spree/testing_support/factories/user_factory.rb

@@ -17,7 +17,10 @@
     end
 
     factory :admin_user do
-      spree_roles { [Spree::Role.find_by(name: 'admin') || create(:role, name: 'admin')] }
+      after(:create) do |user, _|
+        admin_role = Spree::Role.find_by(name: 'admin') || create(:role, name: 'admin')
+        user.spree_roles << admin_role
+      end
     end
 
     factory :user_with_addresses do |_u|

core/spec/models/spree/ability_spec.rb

@@ -59,7 +59,7 @@ def initialize(_user)
     let(:resource) { Object.new }
 
     context 'with admin user' do
-      let(:user) { build :admin_user }
+      let(:user) { create :admin_user }
       it_should_behave_like 'access granted'
       it_should_behave_like 'index allowed'
     end