Propose a new cop BangPersistence

[aliismayilov]

This cop enforces the usage of bang versions of the persistence methods during the rspec setup blocks. The problem with non-bang versions is that it only returns true/false in case of success/failure:

before do
  post.update(non_null_column: nil)
  # => false
end

The above before block fails to setup the desired state, but the developer won't get any feedback about this. Instead, the following version:

before do
  post.update!(non_null_column: nil)
  # => raises ActiveRecord::RecordInvalid
end

This cop has been useful in our company codebase. I'm open to improve it and/or come up with better naming :)

---

Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• Added the new cop to config/default.yml.
• The cop is configured as Enabled: pending in config/default.yml.
• The cop documents examples of good and bad code.
• The tests assert both that bad code is reported and that good code is not reported.
• Set VersionAdded: "<<next>>" in default/config.yml.

If you have modified an existing cop's configuration options:

• Set VersionChanged: "<<next>>" in config/default.yml.

[pirj]

Have you considered making it a more generic cop, targeting rubocop-rails?
It’s not only spec code that suffers from this issue.

[aliismayilov]

Have you considered making it a more generic cop, targeting rubocop-rails? It’s not only spec code that suffers from this issue.

Can you please elaborate?

I can see it being useful in cases where the return value of the persistence call isn't evaluated:

def save_all
  post.update(title: "invalid")
  comments.save
end

In the above case post.update should probably be better handled, but it won't be easy to cover block calls:

save_all do
  post.update(title: "invalid")
end

It's probably hard to tell if the above is properly handled or not, while the code structure is exactly the same as before 🤷