Devise's sign_in test helper is meant to be used only in Controller tests, not in integration ones. For integration specs, we usually do the normal process: sign in the user using capybara by visiting the sign in url and entering valid credentials.
https://groups.google.com/forum/#!topic/plataformatec-devise/0ww5KitMD7g
ログイン処理は visit とかで書くらしい。Controller のテストで使う controller macro は controller のときしか使えないみたい。
