Add a new QA::ElementWithPattern cop

This cop forbids the use of `element :foo, 'pattern'` and
`element :bar, /pattern/` in QA files.
Signed-off-by: Rémy Coutable <remy@rymai.me>

rubocop/cop/qa/element_with_pattern.rb

+require_relative '../../qa_helpers'
+
+module RuboCop
+  module Cop
+    module QA
+      # This cop checks for the usage of factories in migration specs
+      #
+      # @example
+      #
+      #   # bad
+      #   let(:user) { create(:user) }
+      #
+      #   # good
+      #   let(:users) { table(:users) }
+      #   let(:user) { users.create!(name: 'User 1', username: 'user1') }
+      class ElementWithPattern < RuboCop::Cop::Cop
+        include QAHelpers
+
+        MESSAGE = "Don't use a pattern for element, create a corresponding `%s` instead.".freeze
+
+        def on_send(node)
+          return unless in_qa_file?(node)
+          return unless method_name(node).to_s == 'element'
+
+          element_name, pattern = node.arguments
+          return unless pattern
+
+          add_offense(node, location: pattern.source_range, message: MESSAGE % "qa-#{element_name.value.to_s.tr('_', '-')}")
+        end
+
+        private
+
+        def method_name(node)
+          node.children[1]
+        end
+      end
+    end
+  end
+end

rubocop/qa_helpers.rb

+module RuboCop
+  # Module containing helper methods for writing QA cops.
+  module QAHelpers
+    # Returns true if the given node originated from the qa/ directory.
+    def in_qa_file?(node)
+      path = node.location.expression.source_buffer.name
+
+      path.start_with?(File.join(Dir.pwd, 'qa'))
+    end
+  end
+end

rubocop/rubocop.rb

@@ -29,6 +29,7 @@ require_relative 'cop/migration/update_large_table'
 require_relative 'cop/project_path_helper'
 require_relative 'cop/rspec/env_assignment'
 require_relative 'cop/rspec/factories_in_migration_specs'
+require_relative 'cop/qa/element_with_pattern'
 require_relative 'cop/sidekiq_options_queue'
 require_relative 'cop/destroy_all'
 require_relative 'cop/ruby_interpolation_in_translation'

spec/rubocop/cop/qa/element_with_pattern_spec.rb

+require 'spec_helper'
+
+require 'rubocop'
+require 'rubocop/rspec/support'
+
+require_relative '../../../../rubocop/cop/qa/element_with_pattern'
+
+describe RuboCop::Cop::QA::ElementWithPattern do
+  include CopHelper
+
+  let(:source_file) { 'qa/page.rb' }
+
+  subject(:cop) { described_class.new }
+
+  context 'in a QA file' do
+    before do
+      allow(cop).to receive(:in_qa_file?).and_return(true)
+    end
+
+    it "registers an offense for elements with a pattern" do
+      expect_offense(<<-RUBY)
+      view 'app/views/shared/groups/_search_form.html.haml' do
+        element :groups_filter, 'search_field_tag :filter'
+                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ Don't use a pattern for element, create a corresponding `qa-groups-filter` instead.
+        element :groups_filter_placeholder, /Search by name/
+                                            ^^^^^^^^^^^^^^^^ Don't use a pattern for element, create a corresponding `qa-groups-filter-placeholder` instead.
+      end
+      RUBY
+    end
+
+    it "does not register an offense for element without a pattern" do
+      expect_no_offenses(<<-RUBY)
+      view 'app/views/shared/groups/_search_form.html.haml' do
+        element :groups_filter
+        element :groups_filter_placeholder
+      end
+      RUBY
+    end
+  end
+
+  context 'outside of a migration spec file' do
+    it "does not register an offense" do
+      expect_no_offenses(<<-RUBY)
+        describe 'foo' do
+          let(:user) { create(:user) }
+        end
+      RUBY
+    end
+  end
+end

spec/rubocop/qa_helpers_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'rubocop'
+require_relative '../../rubocop/qa_helpers'
+
+describe RuboCop::QAHelpers do
+  def parse_source(source, path = 'foo.rb')
+    buffer = Parser::Source::Buffer.new(path)
+    buffer.source = source
+
+    builder = RuboCop::AST::Builder.new
+    parser = Parser::CurrentRuby.new(builder)
+
+    parser.parse(buffer)
+  end
+
+  let(:cop) do
+    Class.new do
+      include RuboCop::QAHelpers
+    end.new
+  end
+
+  describe '#in_qa_file?' do
+    it 'returns true for a node in the qa/ directory' do
+      node = parse_source('10', Rails.root.join('qa', 'qa', 'page', 'dashboard', 'groups.rb'))
+
+      expect(cop.in_qa_file?(node)).to eq(true)
+    end
+
+    it 'returns false for a node outside the qa/ directory' do
+      node = parse_source('10', Rails.root.join('app', 'foo', 'foo.rb'))
+
+      expect(cop.in_qa_file?(node)).to eq(false)
+    end
+  end
+end