Is DatabaseCleaner still necessary with Rails system specs?

You do not need the DatabaseCleaner gem. Here’s a quick summary of steps you need:

1. Remove capybara-selenium gem and database_cleaner gem
2. Add selenium-webdriver gem
3. Make sure you are using Rails 5.1.5 or later. Earlier versions of Rails 5.1 had a defect in ActionDispatch::SystemTesting::Server that caused problems (fixed here).
4. In your rails_helper file, set config.use_transactional_fixtures = true
5. If you are using Devise for auth, in your rails_helper file, set config.include Devise::Test::IntegrationHelpers, type: :system
6. Set up a basic_configure file as per this post by Noel Rappin.
7. Replace RSpec.feature throughout with RSpec.describe.

See this commit for more details as to how I managed the switch. It was a hassle, but hopefully easier now that 5.1.5 has fixed the ActionDispatch::SystemTesting::Server issue (I had to monkey patch the file in 5.1.4, but you won’t have to now).