Add RepeatedDescription cop

config/default.yml

@@ -137,6 +137,10 @@ RSpec/NotToNot:
   - to_not
   Enabled: true
 
+RSpec/RepeatedDescription:
+  Enabled: true
+  Description: Check for repeated description strings in example groups.
+
 RSpec/SingleArgumentMessageChain:
   Description: Checks that chains of messages contain more than one element.
   Enabled: true

lib/rubocop-rspec.rb

@@ -40,6 +40,7 @@
 require 'rubocop/cop/rspec/named_subject'
 require 'rubocop/cop/rspec/nested_groups'
 require 'rubocop/cop/rspec/not_to_not'
+require 'rubocop/cop/rspec/repeated_description'
 require 'rubocop/cop/rspec/single_argument_message_chain'
 require 'rubocop/cop/rspec/subject_stub'
 require 'rubocop/cop/rspec/verified_doubles'

lib/rubocop/cop/rspec/repeated_description.rb

@@ -0,0 +1,84 @@
+module RuboCop
+  module Cop
+    module RSpec
+      # Check for repeated description strings in example groups.
+      #
+      # @example
+      #
+      #     # bad
+      #     RSpec.describe User do
+      #       it 'is valid' do
+      #         # ...
+      #       end
+      #
+      #       it 'is valid' do
+      #         # ...
+      #       end
+      #     end
+      #
+      #     # good
+      #     RSpec.describe User do
+      #       it 'is valid when first and last name are present' do
+      #         # ...
+      #       end
+      #
+      #       it 'is valid when last name only is present' do
+      #         # ...
+      #       end
+      #     end
+      #
+      class RepeatedDescription < Cop
+        include RuboCop::Cop::ConfigurableEnforcedStyle
+
+        def_node_matcher :example, <<-PATTERN
+          (block $(send _ {#{Examples::ALL.to_node_pattern}} ...) ...)
+        PATTERN
+
+        # Selectors which indicate that indicate we should stop searching
+        SCOPE_CHANGES = ExampleGroups::ALL + SharedGroups::ALL
+
+        # @!method scope_change?(node)
+        #
+        #   Detect if the node is an example or a new example group
+        #
+        def_node_matcher :scope_change?, <<-PATTERN
+          (block (send _ {#{SCOPE_CHANGES.to_node_pattern}} ...) ...)
+        PATTERN
+
+        MSG = 'Repeated description'.freeze
+
+        def on_block(node)
+          return unless example_group?(node)
+
+          repeated_descriptions(node).each do |repeated_hook|
+            add_offense(repeated_hook, :expression)
+          end
+        end
+
+        private
+
+        def repeated_descriptions(node)
+          hooks_in_group(node)
+            .group_by(&:method_args)
+            .reject { |args, _| args.empty? }
+            .values
+            .reject(&:one?)
+            .flatten
+        end
+
+        def hooks_in_group(node, &block)
+          return to_enum(__method__, node) unless block_given?
+
+          node.each_child_node { |child| find_hooks(child, &block) }
+        end
+
+        def find_hooks(node, &block)
+          return if scope_change?(node)
+
+          example(node, &block)
+          hooks_in_group(node, &block)
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/rspec/repeated_description_spec.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+describe RuboCop::Cop::RSpec::RepeatedDescription do
+  subject(:cop) { described_class.new }
+
+  it 'registers an offense for repeated descriptions' do
+    expect_violation(<<-RUBY)
+      describe 'doing x' do
+        it "does x" do
+        ^^^^^^^^^^^ Repeated description
+        end
+
+        it "does x" do
+        ^^^^^^^^^^^ Repeated description
+        end
+      end
+    RUBY
+  end
+end