Add Rails/ResponseParsedBody cop

[r7kamura]

Since Rails 5, there is an often overlooked feature: response.parsed_body.

• Provide @response.parsed_body to work together with post ..., as: :json for testing rails/rails#23594

As a typical pattern, many Rails applications have JSON.parse(response.body) in their controlelr-specs and request-specs, but most of these could be replaced by response.parsed_body. So it would be nice for rubocop-rails to have a Cop that recommends response.parsed_body.

I think there are several advantages to using response.parsed_body.

1. the fact that Rails provides this by default means that Rails would probably encourage the use of it
2. it avoids direct references to JSON
3. shorter code

What do you think?

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[r7kamura]

I addressed the CI failure with the following Pull Request:

• Fix an offense on Style/RedundantRegexpEscape #864

[r7kamura]

Note: At first I created the following Pull Request in rubocop-rspec, but it seemed to be more suitable for rubocop-rails, so I re-created this Cop here.

• Add RSpec/Rails/ResponseParsedBody cop rubocop-rspec#1478

[vlad-pisanov]

Nice! We've been using our own version of this cop in our org for many years. We also correct Oj.load(response.body) (another popular JSON parser) -- but that might be overkill.

[vlad-pisanov]

Add

minimum_target_rails_version 5.0

[koic]

Is Content-Type guaranteed for code before autocorrection? I'm wondering if autocorrection will change Content-Type. So, If Content-Type doesn't change, it looks like there is no change of safety.

[vlad-pisanov]

It's unsafe because the behavior changes a bit.

JSON.parse(body.response) attempts to parse the body as JSON regardless of Content-Type. e.g. if the controller spits out JSON but marks it as application/xml, this will still work. Whereas parsed_body will use the appropriate parser based on Content-Type, and will raise an exception if the response can't be parsed.

https://github.com/rails/rails/blob/282b769fb543404187abde76ca437aa697f6d6ba/actionpack/lib/action_dispatch/testing/test_response.rb#L21-L37

[koic]

I get it. It seems to be an incompatibility behavior potential rather than a false positive potential. So it's unsafe for autocorrection.