I have just wrote and published a little open source ruby gem for rails app, that can help you to test your controllers of active admin using rspec and factory girl.
Feel free to star mark at github page to keep me motivated to update this project:
Github page: https://github.com/sadaf2605/nested_attr Gem: https://rubygems.org/gems/nested_attr
Project Homepage: http://www.sadafnoor.com/nested-attr/
