Add new InternalAffairs/ExampleDescription cop.

The cop checks for examples in rubocop's own RSpec suite where the description does not match the expectation (ie. `expects_offense` with "does not register an offense", etc.).

.rubocop.yml

@@ -130,3 +130,7 @@ Performance/CollectionLiteralInLoop:
 
 RSpec/StubbedMock:
   Enabled: false
+
+InternalAffairs/ExampleDescription:
+  Include:
+    - 'spec/rubocop/cop/**/*.rb'

lib/rubocop/cop/internal_affairs.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative 'internal_affairs/empty_line_between_expect_offense_and_correction'
+require_relative 'internal_affairs/example_description'
 require_relative 'internal_affairs/method_name_equal'
 require_relative 'internal_affairs/node_destructuring'
 require_relative 'internal_affairs/node_type_predicate'

lib/rubocop/cop/internal_affairs/example_description.rb

@@ -0,0 +1,89 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module InternalAffairs
+      # Checks that RSpec examples that use `expects_offense`
+      # or `expects_no_offenses` do not have conflicting
+      # descriptions.
+      #
+      # @example
+      #   # bad
+      #   it 'does not register an offense' do
+      #     expect_offense('...')
+      #   end
+      #
+      #   it 'registers an offense' do
+      #     expect_no_offenses('...')
+      #   end
+      #
+      #   # good
+      #   it 'registers an offense' do
+      #     expect_offense('...')
+      #   end
+      #
+      #   it 'does not register an offense' do
+      #     expect_no_offenses('...')
+      #   end
+      class ExampleDescription < Base
+        class << self
+          attr_accessor :descriptions
+        end
+
+        MSG = 'Description does not match use of `%<method_name>s`.'
+
+        RESTRICT_ON_SEND = %i[
+          expect_offense
+          expect_no_offenses
+          expect_correction
+          expect_no_corrections
+        ].to_set.freeze
+
+        EXPECT_NO_OFFENSES_INCORRECT_DESCRIPTIONS = [
+          /^(adds|registers|reports|finds) (an? )?offense/,
+          /^flags\b/
+        ].freeze
+
+        EXPECT_OFFENSE_INCORRECT_DESCRIPTIONS = [
+          /^(does not|doesn't) (register|find|flag|report)/,
+          /^(does not|doesn't) add (a|an|any )?offense/
+        ].freeze
+
+        EXPECT_NO_CORRECTIONS_INCORRECT_DESCRIPTIONS = [
+          /^(auto[- ]?)?correct/
+        ].freeze
+
+        EXPECT_CORRECTION_INCORRECT_DESCRIPTIONS = [
+          /\b(does not|doesn't) (auto[- ]?)?correct/
+        ].freeze
+
+        def_node_matcher :offense_example?, <<~PATTERN
+          (block
+            (send _ {:it :specify} $_description)
+            _args
+            `(send nil? %RESTRICT_ON_SEND ...)
+          )
+        PATTERN
+
+        def on_send(node)
+          parent = node.each_ancestor(:block).first
+          return unless parent && (description = offense_example?(parent))
+
+          method_name = node.method_name
+          message = format(MSG, method_name: method_name)
+
+          regexp_group = self.class.const_get("#{method_name}_incorrect_descriptions".upcase)
+          check_description(description, regexp_group, message)
+        end
+
+        private
+
+        def check_description(description, regexps, message)
+          return unless regexps.any? { |regexp| regexp.match?(description.value) }
+
+          add_offense(description, message: message)
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/internal_affairs/example_description_spec.rb

@@ -0,0 +1,124 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::InternalAffairs::ExampleDescription, :config do
+  context 'with `expect_offense`' do
+    it 'registers an offense when given an improper description' do
+      expect_offense(<<~RUBY)
+        it 'does not register an offense' do
+           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Description does not match use of `expect_offense`.
+          expect_offense('code')
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when given a proper description' do
+      expect_no_offenses(<<~RUBY)
+        it 'finds an offense' do
+          expect_offense('code')
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when given an unexpected description' do
+      expect_no_offenses(<<~RUBY)
+        it 'foo bar baz' do
+          expect_offense('code')
+        end
+      RUBY
+    end
+  end
+
+  context 'with `expect_no_offenses`' do
+    it 'registers an offense when given an improper description' do
+      expect_offense(<<~RUBY)
+        it 'registers an offense' do
+           ^^^^^^^^^^^^^^^^^^^^^^ Description does not match use of `expect_no_offenses`.
+          expect_no_offenses('code')
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when given a proper description' do
+      expect_no_offenses(<<~RUBY)
+        it 'does not flag' do
+          expect_no_offense('code')
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when given an unexpected description' do
+      expect_no_offenses(<<~RUBY)
+        it 'foo bar baz' do
+          expect_offense('code')
+        end
+      RUBY
+    end
+  end
+
+  context 'with `expect_correction`' do
+    it 'registers an offense when given an improper description' do
+      expect_offense(<<~RUBY)
+        it 'does not auto-correct' do
+           ^^^^^^^^^^^^^^^^^^^^^^^ Description does not match use of `expect_correction`.
+          expect_correction('code', source: 'new code')
+        end
+      RUBY
+    end
+
+    context 'in conjunction with expect_offense' do
+      it 'registers an offense when given an improper description' do
+        expect_offense(<<~RUBY)
+          it 'registers an offense but does not auto-correct' do
+             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Description does not match use of `expect_correction`.
+            expect_offense('code')
+            expect_correction('code')
+          end
+        RUBY
+      end
+
+      context 'when the description is invalid for both methods' do
+        it 'registers an offense for the first method encountered' do
+          expect_offense(<<~RUBY)
+            it 'does not register an offense and does not auto-correct' do
+               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Description does not match use of `expect_offense`.
+              expect_offense('code')
+              expect_correction('code')
+            end
+          RUBY
+        end
+      end
+    end
+  end
+
+  context 'with `expect_no_corrections`' do
+    it 'registers an offense when given an improper description' do
+      expect_offense(<<~RUBY)
+        it 'autocorrects' do
+           ^^^^^^^^^^^^^^ Description does not match use of `expect_no_corrections`.
+          expect_no_corrections
+        end
+      RUBY
+    end
+
+    context 'in conjunction with expect_offense' do
+      it 'registers an offense when given an improper description' do
+        expect_offense(<<~RUBY)
+          it 'auto-corrects' do
+             ^^^^^^^^^^^^^^^ Description does not match use of `expect_no_corrections`.
+            expect_offense('code')
+            expect_no_corrections
+          end
+        RUBY
+      end
+    end
+  end
+
+  context 'when not making an expectation on offenses' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY)
+        it 'registers an offense' do
+        end
+      RUBY
+    end
+  end
+end