Fix deprecation warning for :unprocessable_entity in scaffold-generated tests with Rack 3.2

[taketo1113]

This Pull Request updates the scaffold and scaffold_controller templates to resolve the following warning that occurs when running the generated tests.

/path-to-app/vendor/bundle/ruby/3.4.0/gems/rspec-rails-8.0.1/lib/rspec/rails/matchers/have_http_status.rb:219: warning: Status code :unprocessable_entity is deprecated and will be removed in a future version of Rack. Please use :unprocessable_content instead.

Fix #2859

Details

It updates the scaffold and scaffold_controller templates for the invalid params cases in #create / #update within request specs and controller specs.

This change modifies lines like expect(response).to have_http_status(:unprocessable_entity) in the following kind of code:

# spec/requests/posts_spec.rb
  describe "POST /create" do
...
    context "with invalid parameters" do
...
      it "renders a response with 422 status (i.e. to display the 'new' template)" do
        post posts_url, params: { post: invalid_attributes }
        expect(response).to have_http_status(:unprocessable_entity)
      end
    end
  end

For rack 3.1 and higher, this change uses :unprocessable_content instead of :unprocessable_entity.
For rack 3.0 and below, it continues to use :unprocessable_entity.
This is because :unprocessable_content was introduced in rack 3.1:
rack/rack#2137

The symbol selection between :unprocessable_entity and :unprocessable_content is handled using Rack::Utils::SYMBOL_TO_STATUS_CODE.key(422).

The behavior of Rack::Utils::SYMBOL_TO_STATUS_CODE.key(422) varies depending on the rack version:

Rack::Utils::SYMBOL_TO_STATUS_CODE.key(422)
=> :unprocessable_content # rack 3.1 or higher
=> :unprocessable_entity # rack 3.0 and below

The code for Rack::Utils::SYMBOL_TO_STATUS_CODE can be found here:
https://github.com/rack/rack/blob/79d6820b73d9084a60ec1f9912e3ab00439bd5d3/lib/rack/utils.rb#L564-L566

[taketo1113]

The failing tests for Rails main / Rails ~> 8.0.0 in CI should pass once the following commit is merged:

741488e

# spec/rspec/rails/matchers/have_http_status_spec.rb
  context 'with deprecated rack status codes' do
    it 'supports the original names' do
+      allow(Rack::Utils).to receive(:warn).with(/unprocessable_entity is deprecated/, anything)
      expect(create_response(status: 422)).to have_http_status(:unprocessable_entity)
    end
  end

[JonRowe]

You can cherry pick that commit to make this pass

[taketo1113]

@JonRowe Thanks for the comment.

I cherry-picked that commit and the tests passed.

[JonRowe]

Thanks!

[JonRowe]

Released in 8.0.2