Expose files to support testing Cops using RSpec (rubocop#3179)

The exposed files can be loaded from spec_helper using:

    require 'rubocop/rspec/support'

CHANGELOG.md

@@ -14,6 +14,7 @@
 * [#3173](https://github.com/bbatsov/rubocop/pull/3173): Make `Style/ModuleFunction` configurable with `module_function` and `extend_self` styles. ([@tjwp][])
 * [#3105](https://github.com/bbatsov/rubocop/issues/3105): Add new `Style/RequestReferer` cop. ([@giannileggio][])
 * [#3200](https://github.com/bbatsov/rubocop/pull/3200): Add autocorrect for `Style/EachForSimpleLoop` cop. ([@tejasbubane][])
+* [#3179](https://github.com/bbatsov/rubocop/pull/3179): Expose files to support testings Cops using RSpec. ([@tjwp][])
 
 ### Bug fixes
 

spec/support/cop_helper.rb → lib/rubocop/rspec/cop_helper.rb

@@ -3,6 +3,7 @@
 
 require 'tempfile'
 
+# This module provides methods that make it easier to test Cops.
 module CopHelper
   extend RSpec::SharedContext
 
@@ -64,6 +65,8 @@ def _investigate(cop, processed_source)
 
 module RuboCop
   module Cop
+    # Monkey-patch Cop for tests to provide easy access to messages and
+    # highlights.
     class Cop
       def messages
         offenses.sort.map(&:message)

lib/rubocop/rspec/support.rb

@@ -0,0 +1,9 @@
+# encoding: utf-8
+# frozen_string_literal: true
+
+# Require this file to load code that supports testing using RSpec.
+
+require 'rubocop/rspec/cop_helper'
+require 'rubocop/rspec/host_environment_simulation_helper'
+require 'rubocop/rspec/shared_contexts'
+require 'rubocop/rspec/shared_examples'

spec/spec_helper.rb

@@ -12,6 +12,9 @@
 
 require 'webmock/rspec'
 
+# Require supporting files exposed for testing.
+require 'rubocop/rspec/support'
+
 # Requires supporting files with custom matchers and macros, etc,
 # in ./support/ and its subdirectories.
 Dir["#{File.dirname(__FILE__)}/support/**/*.rb"].each { |f| require f }