https://minitestrails.com/blog/testing-user-registration-rails-minitest/

Rails 8’s bin/rails generate authentication gives you sign-in, sign-out, and password reset but it does not give you a way to register new users to the app. In this post you will add the registration feature and test it with Minitest:

• Model validations for registration rules
• Integration tests to cover all edge cases for registration flow
• Smoke-styled system test for happy path: visit registration page, add correct input details, submit and get signed in to the app after registration.