Add project specs for config/default.yml

This PR imports several project specs from RuboCop core.

config/default.yml

@@ -92,15 +92,15 @@ Performance/EndWith:
   VersionChanged: '0.44'
 
 Performance/FixedSize:
-  Description: 'Do not compute the size of statically sized objects except in constants'
+  Description: 'Do not compute the size of statically sized objects except in constants.'
   Enabled: true
   VersionAdded: '0.35'
 
 Performance/FlatMap:
   Description: >-
                   Use `Enumerable#flat_map`
                   instead of `Enumerable#map...Array#flatten(1)`
-                  or `Enumberable#collect..Array#flatten(1)`
+                  or `Enumberable#collect..Array#flatten(1)`.
   Reference: 'https://github.com/JuanitoFatas/fast-ruby#enumerablemaparrayflatten-vs-enumerableflat_map-code'
   Enabled: true
   VersionAdded: '0.30'
@@ -111,7 +111,7 @@ Performance/FlatMap:
   # `flatten` without any parameters can flatten multiple levels.
 
 Performance/InefficientHashSearch:
-  Description: 'Use `key?` or `value?` instead of `keys.include?` or `values.include?`'
+  Description: 'Use `key?` or `value?` instead of `keys.include?` or `values.include?`.'
   Reference: 'https://github.com/JuanitoFatas/fast-ruby#hashkey-instead-of-hashkeysinclude-code'
   Enabled: true
   VersionAdded: '0.56'

spec/project_spec.rb

@@ -1,6 +1,81 @@
 # frozen_string_literal: true
 
 RSpec.describe 'RuboCop Performance Project', type: :feature do
+  describe 'default configuration file' do
+    subject(:config) { RuboCop::ConfigLoader.load_file('config/default.yml') }
+
+    let(:registry) { RuboCop::Cop::Cop.registry }
+    let(:cop_names) do
+      registry.with_department(:Performance).cops.map(&:cop_name)
+    end
+
+    let(:configuration_keys) { config.keys }
+
+    it 'has a nicely formatted description for all cops' do
+      cop_names.each do |name|
+        description = config[name]['Description']
+        expect(description.nil?).to be(false)
+        expect(description).not_to include("\n")
+      end
+    end
+
+    it 'requires a nicely formatted `VersionAdded` metadata for all cops' do
+      cop_names.each do |name|
+        version = config[name]['VersionAdded']
+        expect(version.nil?).to(be(false),
+                                "VersionAdded is required for #{name}.")
+        expect(version).to(match(/\A\d+\.\d+\z/),
+                           "#{version} should be format ('X.Y') for #{name}.")
+      end
+    end
+
+    it 'have a period at EOL of description' do
+      cop_names.each do |name|
+        description = config[name]['Description']
+
+        expect(description).to match(/\.\z/)
+      end
+    end
+
+    it 'sorts configuration keys alphabetically' do
+      expected = configuration_keys.sort
+      configuration_keys.each_with_index do |key, idx|
+        expect(key).to eq expected[idx]
+      end
+    end
+
+    it 'has a SupportedStyles for all EnforcedStyle ' \
+      'and EnforcedStyle is valid' do
+      errors = []
+      cop_names.each do |name|
+        enforced_styles = config[name]
+                          .select { |key, _| key.start_with?('Enforced') }
+        enforced_styles.each do |style_name, style|
+          supported_key = RuboCop::Cop::Util.to_supported_styles(style_name)
+          valid = config[name][supported_key]
+          unless valid
+            errors.push("#{supported_key} is missing for #{name}")
+            next
+          end
+          next if valid.include?(style)
+
+          errors.push("invalid #{style_name} '#{style}' for #{name} found")
+        end
+      end
+
+      raise errors.join("\n") unless errors.empty?
+    end
+
+    it 'does not have nay duplication' do
+      fname = File.expand_path('../config/default.yml', __dir__)
+      content = File.read(fname)
+      RuboCop::YAMLDuplicationChecker.check(content, fname) do |key1, key2|
+        raise "#{fname} has duplication of #{key1.value} " \
+              "on line #{key1.start_line} and line #{key2.start_line}"
+      end
+    end
+  end
+
   describe 'changelog' do
     subject(:changelog) do
       path = File.join(File.dirname(__FILE__), '..', 'CHANGELOG.md')