diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..c87090f
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,36 @@
+name: Ruby
+
+on:
+  push:
+    branches:
+    - main
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        ruby-version:
+          - '3.0'
+          - '3.1'
+          - '3.2'
+          - '3.3'
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby-version }}
+          bundler-cache: true
+
+      - name: Run specs
+        run: |
+          bin/rspec
+
+      - name: Lint with standard
+        run: |
+          bin/standardrb
diff --git a/.gitignore b/.gitignore
index b8479b7..87a5af7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,8 @@ pkg/*
 .rvmrc
 log/*.log
 tmp/
+
+# rspec failure tracking
+.rspec_status
+
+/coverage/
diff --git a/.rspec b/.rspec
index 5f16476..2559e39 100644
--- a/.rspec
+++ b/.rspec
@@ -1,2 +1,3 @@
 --color
 --format progress
+--require spec_helper
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 8e1084c..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,9 +0,0 @@
-language: ruby
-cache: bundler
-sudo: false
-rvm:
-  - 2.0.0
-  - 2.1
-  - 2.2.5
-  - 2.3.1
-script: bundle exec rspec spec
diff --git a/Gemfile b/Gemfile
index b4e2a20..60001ee 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,12 @@
 source "https://rubygems.org"
 
 gemspec
+
+gem "combustion"
+gem "rack-test"
+gem "rails", "> 6"
+gem "rake"
+gem "rspec-rails"
+gem "rspec"
+gem "simplecov", require: false
+gem "standard"
diff --git a/Guardfile b/Guardfile
deleted file mode 100644
index 135f0e6..0000000
--- a/Guardfile
+++ /dev/null
@@ -1,8 +0,0 @@
-#!/usr/bin/env ruby
-
-guard 'rspec', :cli => "-fd", :version => 2 do
-  watch(%r{^spec/.+_spec\.rb$})
-  watch(%r{^lib/(.+)\.rb$})     { "spec" }
-  watch('spec/spec_helper.rb')  { "spec" }
-end
-
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..10f2327
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2024
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
index c5103d3..f5de189 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,15 @@
-# HttpAcceptLanguage [![Build Status](https://travis-ci.org/iain/http_accept_language.svg?branch=master)](https://travis-ci.org/iain/http_accept_language)
+# HttpAcceptLanguage
 
-A gem which helps you detect the users preferred language, as sent by the "Accept-Language" HTTP header.
+A gem which helps you detect the users preferred language, as sent by the
+"Accept-Language" HTTP header.
 
-The algorithm is based on [RFC 2616](http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html), with one exception:
-when a user requests "en-US" and "en" is an available language, "en" is deemed compatible with "en-US".
-The RFC specifies that the requested language must either exactly match the available language or must exactly match a prefix of the available language. This means that when the user requests "en" and "en-US" is available, "en-US" would be compatible, but not the other way around. This is usually not what you're looking for.
+The algorithm is based on [RFC 2616], with one exception: when a user requests
+`en-US` and `en` is an available language, `en` is deemed compatible with
+`en-US`. The RFC specifies that the requested language must either exactly match
+the available language or must exactly match a prefix of the available language.
+This means that when the user requests `en` and `en-US` is available, `en-US`
+would be compatible, but not the other way around. This is usually not what
+you're looking for.
 
 Since version 2.0, this gem is Rack middleware.
 
@@ -30,11 +35,11 @@ class SomeController < ApplicationController
 end
 ```
 
-You can easily set the locale used for i18n in a before-filter:
+You can easily set the locale used for i18n with a filter:
 
 ```ruby
 class SomeController < ApplicationController
-  before_filter :set_locale
+  before_action :set_locale
 
   private
     def set_locale
@@ -43,12 +48,11 @@ class SomeController < ApplicationController
 end
 ```
 
-If you want to enable this behavior by default in your controllers, you can just include the provided concern:
+To enable this behavior by default, include the provided concern:
 
 ```ruby
 class ApplicationController < ActionController::Base
   include HttpAcceptLanguage::AutoLocale
-
 #...
 end
 ```
@@ -88,21 +92,21 @@ end
 
 ## Available methods
 
-* **user_preferred_languages**:
-  Returns a sorted array based on user preference in HTTP_ACCEPT_LANGUAGE, sanitized and all.
-* **preferred_language_from(languages)**:
-  Finds the locale specifically requested by the browser
-* **compatible_language_from(languages)**:
-  Returns the first of the user_preferred_languages that is compatible with the available locales.
+* **user_preferred_languages**: Returns a sorted array based on user preference
+  in `HTTP_ACCEPT_LANGUAGE`, sanitized and all.
+* **preferred_language_from(languages)**: Finds the locale specifically
+  requested by the browser.
+* **compatible_language_from(languages)**: Returns the first of the
+  `user_preferred_languages` that is compatible with the available locales.
   Ignores region.
-* **sanitize_available_locales(languages)**:
-  Returns a supplied list of available locals without any extra application info
-  that may be attached to the locale for storage in the application.
-* **language_region_compatible_from(languages)**:
-  Returns the first of the user preferred languages that is
-  also found in available languages.  Finds best fit by matching on
-  primary language first and secondarily on region.  If no matching region is
-  found, return the first language in the group matching that primary language.
+* **sanitize_available_locales(languages)**: Returns a supplied list of
+  available locales without any extra application info that may be attached to
+  the locale for storage in the application.
+* **language_region_compatible_from(languages)**: Returns the first of the user
+  preferred languages that is also found in available languages.  Finds best fit
+  by matching on primary language first and secondarily on region.  If no
+  matching region is found, return the first language in the group matching that
+  primary language.
 
 ## Installation
 
@@ -122,4 +126,6 @@ Run `bundle install` to install it.
 
 ---
 
-Released under the MIT license
+Released under the MIT license.
+
+[RFC 2616]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
\ No newline at end of file
diff --git a/Rakefile b/Rakefile
index 1b92817..c5c746e 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,13 +1,6 @@
 require "bundler/gem_tasks"
 
-require 'rspec/core/rake_task'
+require "rspec/core/rake_task"
 RSpec::Core::RakeTask.new(:spec)
 
-require 'cucumber/rake/task'
-Cucumber::Rake::Task.new(:cucumber)
-
-Cucumber::Rake::Task.new(:wip, "Run features tagged with @wip") do |t|
-  t.profile = "wip"
-end
-
-task :default => [:spec, :cucumber, :wip]
+task default: [:spec]
diff --git a/bin/rspec b/bin/rspec
new file mode 100755
index 0000000..cb53ebe
--- /dev/null
+++ b/bin/rspec
@@ -0,0 +1,27 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+#
+# This file was generated by Bundler.
+#
+# The application 'rspec' is installed as part of a gem, and
+# this file is here to facilitate running it.
+#
+
+ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
+
+bundle_binstub = File.expand_path("bundle", __dir__)
+
+if File.file?(bundle_binstub)
+  if File.read(bundle_binstub, 300).include?("This file was generated by Bundler")
+    load(bundle_binstub)
+  else
+    abort("Your `bin/bundle` was not generated by Bundler, so this binstub cannot run.
+Replace `bin/bundle` by running `bundle binstubs bundler --force`, then run this command again.")
+  end
+end
+
+require "rubygems"
+require "bundler/setup"
+
+load Gem.bin_path("rspec-core", "rspec")
diff --git a/bin/setup b/bin/setup
new file mode 100755
index 0000000..dce67d8
--- /dev/null
+++ b/bin/setup
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here
diff --git a/bin/standardrb b/bin/standardrb
new file mode 100755
index 0000000..b329561
--- /dev/null
+++ b/bin/standardrb
@@ -0,0 +1,27 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+#
+# This file was generated by Bundler.
+#
+# The application 'standardrb' is installed as part of a gem, and
+# this file is here to facilitate running it.
+#
+
+ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
+
+bundle_binstub = File.expand_path("bundle", __dir__)
+
+if File.file?(bundle_binstub)
+  if File.read(bundle_binstub, 300).include?("This file was generated by Bundler")
+    load(bundle_binstub)
+  else
+    abort("Your `bin/bundle` was not generated by Bundler, so this binstub cannot run.
+Replace `bin/bundle` by running `bundle binstubs bundler --force`, then run this command again.")
+  end
+end
+
+require "rubygems"
+require "bundler/setup"
+
+load Gem.bin_path("standard", "standardrb")
diff --git a/config.ru b/config.ru
new file mode 100644
index 0000000..1265db9
--- /dev/null
+++ b/config.ru
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require "rubygems"
+require "bundler"
+
+Bundler.require :default, :development
+
+Combustion.initialize! :all
+run Combustion::Application
diff --git a/cucumber.yml b/cucumber.yml
deleted file mode 100644
index 0c12ef1..0000000
--- a/cucumber.yml
+++ /dev/null
@@ -1,2 +0,0 @@
-default: --format progress --strict --tags ~@wip
-wip: --format pretty --wip --tags @wip
diff --git a/features/rails_integration.feature b/features/rails_integration.feature
deleted file mode 100644
index 99d8433..0000000
--- a/features/rails_integration.feature
+++ /dev/null
@@ -1,29 +0,0 @@
-@rails
-Feature: Rails Integration
-
-  To use http_accept_language inside a Rails application, just add it to your
-  Gemfile and run `bundle install`.
-
-  It is automatically added to your middleware.
-
-  Scenario: Installing
-    When I generate a new Rails app
-    And I add http_accept_language to my Gemfile
-    And I run `rake middleware`
-    Then the output should contain "use HttpAcceptLanguage::Middleware"
-
-  Scenario: Using
-    Given I have installed http_accept_language
-    When I generate the following controller:
-    """
-    class LanguagesController < ApplicationController
-
-      def index
-        languages = http_accept_language.user_preferred_languages
-        render :text => "Languages: #{languages.join(' : ')}"
-      end
-
-    end
-    """
-    When I access that action with the HTTP_ACCEPT_LANGUAGE header "en-us,en-gb;q=0.8,en;q=0.6,es-419"
-    Then the response should contain "Languages: en-US : es-419 : en-GB : en"
diff --git a/features/steps/rails.rb b/features/steps/rails.rb
deleted file mode 100644
index bba48fc..0000000
--- a/features/steps/rails.rb
+++ /dev/null
@@ -1,37 +0,0 @@
-Before "@rails" do
-  @rails = RailsDriver.new
-end
-
-When /^I generate a new Rails app$/ do
-  @rails.generate_rails
-end
-
-When /^I add http_accept_language to my Gemfile$/ do
-  @rails.append_gemfile
-end
-
-Given /^I have installed http_accept_language$/ do
-  @rails.install_gem
-end
-
-When /^I generate the following controller:$/ do |string|
-  @rails.generate_controller "languages", string
-end
-
-When /^I access that action with the HTTP_ACCEPT_LANGUAGE header "(.*?)"$/ do |header|
-  @rails.with_rails_running do
-    @rails.request_with_http_accept_language_header(header, "/languages")
-  end
-end
-
-Then /^the response should contain "(.*?)"$/ do |output|
-  @rails.output_should_contain(output)
-end
-
-When /^I run `rake middleware`$/ do
-  @rails.bundle_exec("rake middleware")
-end
-
-Then /^the output should contain "(.*?)"$/ do |expected|
-  @rails.assert_partial_output(expected, @rails.all_output)
-end
diff --git a/features/support/rails_driver.rb b/features/support/rails_driver.rb
deleted file mode 100644
index eaf2b37..0000000
--- a/features/support/rails_driver.rb
+++ /dev/null
@@ -1,93 +0,0 @@
-require 'aruba/api'
-
-class RailsDriver
-  include Aruba::Api
-
-  def initialize
-    @aruba_io_wait_seconds = 10
-    # @announce_stdout = true
-    # @announce_stderr = true
-    # @announce_cmd = true
-    # @announce_dir = true
-    # @announce_env = true
-  end
-
-  def app_name
-    "foobar"
-  end
-
-  def install_gem
-    if app_exists?
-      cd app_name
-    else
-      generate_rails
-      append_gemfile
-    end
-  end
-
-  def app_exists?
-    in_current_dir do
-      File.exist?("#{app_name}/Gemfile")
-    end
-  end
-
-  def bundle_exec(cmd)
-    run_simple "bundle exec #{cmd}"
-  end
-
-  def generate_rails
-    # install rails with as few things as possible, for speed!
-    bundle_exec "rails new #{app_name} --force --skip-git --skip-active-record --skip-sprockets --skip-javascript --skip-test-unit --old-style-hash"
-    cd app_name
-  end
-
-  def append_gemfile
-    # Specifiy a path so cucumber will use the unreleased version of the gem
-    append_to_file "Gemfile", "gem 'http_accept_language', :path => '#{gem_path}'"
-  end
-
-  def gem_path
-    File.expand_path('../../../', __FILE__)
-  end
-
-  def generate_controller(name, content)
-    bundle_exec "rails generate resource #{name} --force"
-    write_file "app/controllers/#{name}_controller.rb", content
-  end
-
-  def request_with_http_accept_language_header(header, path)
-    run_simple "curl  --retry 10 -H 'Accept-language: #{header}' #{File.join(host, path)} -o #{response}"
-    run_simple "cat out.html"
-  end
-
-  def host
-    "http://localhost:13000"
-  end
-
-  def with_rails_running
-    start_rails
-    yield
-  ensure
-    stop_rails
-  end
-
-  def start_rails
-    bundle_exec "rails server -p 13000 -d"
-  end
-
-  def stop_rails
-    in_current_dir do
-      `cat tmp/pids/server.pid | xargs kill -9`
-    end
-  end
-
-  def response
-    File.expand_path(File.join(current_dir, 'out.html'))
-  end
-
-  def output_should_contain(expected)
-    actual = File.open(response, 'r:utf-8').read
-    actual.should include expected
-  end
-
-end
diff --git a/http_accept_language.gemspec b/http_accept_language.gemspec
index 5885f8a..d777008 100644
--- a/http_accept_language.gemspec
+++ b/http_accept_language.gemspec
@@ -1,30 +1,22 @@
-# -*- encoding: utf-8 -*-
-$:.push File.expand_path("../lib", __FILE__)
-require "http_accept_language/version"
+require_relative "lib/http_accept_language/version"
 
-Gem::Specification.new do |s|
-  s.name        = "http_accept_language"
-  s.version     = HttpAcceptLanguage::VERSION
-  s.authors     = ["iain"]
-  s.email       = ["iain@iain.nl"]
-  s.homepage    = "https://github.com/iain/http_accept_language"
-  s.summary     = %q{Find out which locale the user preferes by reading the languages they specified in their browser}
-  s.description = %q{Find out which locale the user preferes by reading the languages they specified in their browser}
-  s.license     = "MIT"
+Gem::Specification.new do |spec|
+  spec.authors = ["iain"]
+  spec.email = ["iain@iain.nl"]
+  spec.homepage = "https://github.com/iain/http_accept_language"
+  spec.license = "MIT"
+  spec.name = "http_accept_language"
+  spec.required_ruby_version = ">= 3.0.0"
+  spec.summary = "Find out which locale the user prefers by reading the languages they specified in their browser."
+  spec.version = HttpAcceptLanguage::VERSION
 
-  s.rubyforge_project = "http_accept_language"
+  spec.files = Dir[
+    "lib/**/*",
+    "README.md",
+    "LICENSE.txt",
+  ]
 
-  s.files         = `git ls-files`.split("\n")
-  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
-  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
-  s.require_paths = ["lib"]
-
-  s.add_development_dependency 'rake'
-  s.add_development_dependency 'rspec'
-  s.add_development_dependency 'rack-test'
-  s.add_development_dependency 'guard-rspec'
-  s.add_development_dependency 'listen', '< 3.1.0' if RUBY_VERSION < '2.2.5'
-  s.add_development_dependency 'rails', ['>= 3.2.6', *('< 5' if RUBY_VERSION < '2.2.2')]
-  s.add_development_dependency 'cucumber'
-  s.add_development_dependency 'aruba'
+  spec.bindir = "exe"
+  spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
 end
diff --git a/lib/http_accept_language.rb b/lib/http_accept_language.rb
index 0e8a0a6..a91f21a 100644
--- a/lib/http_accept_language.rb
+++ b/lib/http_accept_language.rb
@@ -1,4 +1,4 @@
-require 'http_accept_language/auto_locale'
-require 'http_accept_language/parser'
-require 'http_accept_language/middleware'
-require 'http_accept_language/railtie' if defined?(Rails::Railtie)
+require "http_accept_language/auto_locale"
+require "http_accept_language/parser"
+require "http_accept_language/middleware"
+require "http_accept_language/railtie" if defined?(Rails::Railtie)
diff --git a/lib/http_accept_language/auto_locale.rb b/lib/http_accept_language/auto_locale.rb
index 82490eb..73cf45c 100644
--- a/lib/http_accept_language/auto_locale.rb
+++ b/lib/http_accept_language/auto_locale.rb
@@ -1,15 +1,11 @@
-require 'active_support/concern'
+require "active_support/concern"
 
 module HttpAcceptLanguage
   module AutoLocale
     extend ActiveSupport::Concern
 
     included do
-      if respond_to?(:prepend_before_action)
-        prepend_before_action :set_locale
-      else
-        prepend_before_filter :set_locale
-      end
+      prepend_before_action :set_locale
     end
 
     private
diff --git a/lib/http_accept_language/middleware.rb b/lib/http_accept_language/middleware.rb
index 6f42e1a..3998bf8 100644
--- a/lib/http_accept_language/middleware.rb
+++ b/lib/http_accept_language/middleware.rb
@@ -6,11 +6,11 @@ def initialize(app)
 
     def call(env)
       env["http_accept_language.parser"] = Parser.new(env["HTTP_ACCEPT_LANGUAGE"])
-      
+
       def env.http_accept_language
         self["http_accept_language.parser"]
       end
-      
+
       @app.call(env)
     end
   end
diff --git a/lib/http_accept_language/parser.rb b/lib/http_accept_language/parser.rb
index f7e4086..ecb67bf 100644
--- a/lib/http_accept_language/parser.rb
+++ b/lib/http_accept_language/parser.rb
@@ -1,5 +1,8 @@
 module HttpAcceptLanguage
   class Parser
+    DEFAULT_QUALITY = 1.0
+    LOCALE_FORMAT = /^[a-z\-0-9]+|\*$/i
+
     attr_accessor :header
 
     def initialize(header)
@@ -7,7 +10,6 @@ def initialize(header)
     end
 
     # Returns a sorted array based on user preference in HTTP_ACCEPT_LANGUAGE.
-    # Browsers send this HTTP header, so don't think this is holy.
     #
     # Example:
     #
@@ -16,31 +18,29 @@ def initialize(header)
     #
     def user_preferred_languages
       @user_preferred_languages ||= begin
-        header.to_s.gsub(/\s+/, '').split(',').map do |language|
-          locale, quality = language.split(';q=')
-          raise ArgumentError, 'Not correctly formatted' unless locale =~ /^[a-z\-0-9]+|\*$/i
+        languages_from_header.map do |language|
+          locale, quality = language.split(";q=")
+          raise ArgumentError, "Not correctly formatted" unless LOCALE_FORMAT.match?(locale)
 
-          locale  = locale.downcase.gsub(/-[a-z0-9]+$/i, &:upcase) # Uppercase territory
-          locale  = nil if locale == '*' # Ignore wildcards
+          locale = locale.downcase.gsub(/-[a-z0-9]+$/i, &:upcase) # Uppercase territory
+          locale = nil if locale == "*" # Ignore wildcards
 
-          quality = quality ? quality.to_f : 1.0
+          quality = quality ? quality.to_f : DEFAULT_QUALITY
 
           [locale, quality]
         end.sort do |(_, left), (_, right)|
           right <=> left
         end.map(&:first).compact
-      rescue ArgumentError # Just rescue anything if the browser messed up badly.
+      rescue ArgumentError # Rescue from malformed language strings.
         []
       end
     end
 
     # Sets the user languages preference, overriding the browser
     #
-    def user_preferred_languages=(languages)
-      @user_preferred_languages = languages
-    end
+    attr_writer :user_preferred_languages
 
-    # Finds the locale specifically requested by the browser.
+    # Finds the first locale specifically requested by the browser.
     #
     # Example:
     #
@@ -59,22 +59,22 @@ def preferred_language_from(array)
     #   request.compatible_language_from I18n.available_locales
     #
     def compatible_language_from(available_languages)
-      user_preferred_languages.map do |preferred| #en-US
+      user_preferred_languages.map do |preferred| # en-US
         preferred = preferred.downcase
-        preferred_language = preferred.split('-', 2).first
+        preferred_language = preferred.split("-", 2).first
 
         available_languages.find do |available| # en
           available = available.to_s.downcase
-          preferred == available || preferred_language == available.split('-', 2).first
+          preferred == available || preferred_language == available.split("-", 2).first
         end
       end.compact.first
     end
 
-    # Returns a supplied list of available locals without any extra application info
-    # that may be attached to the locale for storage in the application.
+    # Returns a supplied list of available locales without any extra application
+    # info that may be attached to the locale for storage in the application.
     #
-    # Example:
-    # [ja_JP-x1, en-US-x4, en_UK-x5, fr-FR-x3] => [ja-JP, en-US, en-UK, fr-FR]
+    # Example: [ja_JP-x1, en-US-x4, en_UK-x5, fr-FR-x3] => [ja-JP, en-US, en-UK,
+    # fr-FR]
     #
     def sanitize_available_locales(available_languages)
       available_languages.map do |available|
@@ -82,10 +82,10 @@ def sanitize_available_locales(available_languages)
       end
     end
 
-    # Returns the first of the user preferred languages that is
-    # also found in available languages.  Finds best fit by matching on
-    # primary language first and secondarily on region.  If no matching region is
-    # found, return the first language in the group matching that primary language.
+    # Returns the first of the user preferred languages that is also found in
+    # available languages.  Finds best fit by matching on primary language first
+    # and then on region.  If no matching region is found, return the first
+    # language in the group matching that primary language.
     #
     # Example:
     #
@@ -93,16 +93,25 @@ def sanitize_available_locales(available_languages)
     #
     def language_region_compatible_from(available_languages)
       available_languages = sanitize_available_locales(available_languages)
-      user_preferred_languages.map do |preferred| #en-US
+      user_preferred_languages.map do |preferred| # en-US
         preferred = preferred.downcase
-        preferred_language = preferred.split('-', 2).first
+        preferred_language = preferred.split("-", 2).first
 
         lang_group = available_languages.select do |available| # en
-          preferred_language == available.downcase.split('-', 2).first
+          preferred_language == available.downcase.split("-", 2).first
         end
-        
-        lang_group.find { |lang| lang.downcase == preferred } || lang_group.first #en-US, en-UK
+
+        lang_group.find { |lang| lang.downcase == preferred } || lang_group.first # en-US, en-UK
       end.compact.first
     end
+
+    private
+
+    def languages_from_header
+      header
+        .to_s
+        .gsub(/\s+/, "")
+        .split(",")
+    end
   end
 end
diff --git a/lib/http_accept_language/version.rb b/lib/http_accept_language/version.rb
index 36a2f9b..805da0b 100644
--- a/lib/http_accept_language/version.rb
+++ b/lib/http_accept_language/version.rb
@@ -1,3 +1,3 @@
 module HttpAcceptLanguage
-  VERSION = '2.1.1'
+  VERSION = "2.1.1"
 end
diff --git a/spec/auto_locale_spec.rb b/spec/auto_locale_spec.rb
index 8679f25..ee0f306 100644
--- a/spec/auto_locale_spec.rb
+++ b/spec/auto_locale_spec.rb
@@ -1,24 +1,11 @@
-require 'i18n'
-require 'http_accept_language/auto_locale'
-require 'http_accept_language/parser'
-require 'http_accept_language/middleware'
-
-describe HttpAcceptLanguage::AutoLocale do
+RSpec.describe HttpAcceptLanguage::AutoLocale do
   let(:controller_class) do
-    Class.new do
+    Class.new(ActionController::Base) do
       def initialize(header = nil)
         super()
         @header = header
       end
 
-      def self.prepend_before_action(dummy)
-        # dummy method
-      end
-
-      def self.prepend_before_filter(dummy)
-        # dummy method
-      end
-
       def http_accept_language
         @http_accept_language ||= HttpAcceptLanguage::Parser.new(@header)
       end
@@ -54,7 +41,7 @@ def http_accept_language
     end
   end
 
-  let(:no_accept_language_controller) { controller_class.new() }
+  let(:no_accept_language_controller) { controller_class.new }
 
   context "default locale is ja" do
     before do
diff --git a/spec/internal/app/controllers/application_controller.rb b/spec/internal/app/controllers/application_controller.rb
new file mode 100644
index 0000000..09705d1
--- /dev/null
+++ b/spec/internal/app/controllers/application_controller.rb
@@ -0,0 +1,2 @@
+class ApplicationController < ActionController::Base
+end
diff --git a/spec/internal/app/controllers/languages_controller.rb b/spec/internal/app/controllers/languages_controller.rb
new file mode 100644
index 0000000..d909cde
--- /dev/null
+++ b/spec/internal/app/controllers/languages_controller.rb
@@ -0,0 +1,11 @@
+class LanguagesController < ApplicationController
+  def index
+    render plain: "Languages: #{languages.join(" : ")}"
+  end
+
+  private
+
+  def languages
+    http_accept_language.user_preferred_languages
+  end
+end
diff --git a/spec/internal/config/routes.rb b/spec/internal/config/routes.rb
new file mode 100644
index 0000000..1502766
--- /dev/null
+++ b/spec/internal/config/routes.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+Rails.application.routes.draw do
+  root to: "languages#index"
+end
diff --git a/spec/internal/log/.gitignore b/spec/internal/log/.gitignore
new file mode 100644
index 0000000..bf0824e
--- /dev/null
+++ b/spec/internal/log/.gitignore
@@ -0,0 +1 @@
+*.log
\ No newline at end of file
diff --git a/spec/middleware_spec.rb b/spec/middleware_spec.rb
index 931de7c..aaefbe6 100644
--- a/spec/middleware_spec.rb
+++ b/spec/middleware_spec.rb
@@ -1,24 +1,18 @@
-require 'http_accept_language'
-require 'rack/test'
-require 'json'
-
 class TestRackApp
-
   def call(env)
     request = Rack::Request.new(env)
     http_accept_language = env.http_accept_language
     result = {
-      :user_preferred_languages => http_accept_language.user_preferred_languages,
+      user_preferred_languages: http_accept_language.user_preferred_languages
     }
-    if request.params['preferred']
-      result[:preferred_language_from] = http_accept_language.preferred_language_from(request.params['preferred'])
+    if request.params["preferred"]
+      result[:preferred_language_from] = http_accept_language.preferred_language_from(request.params["preferred"])
     end
-    [ 200, {}, [ JSON.generate(result) ]]
+    [200, {}, [JSON.generate(result)]]
   end
-
 end
 
-describe "Rack integration" do
+RSpec.describe "Rack integration" do
   include Rack::Test::Methods
 
   def app
@@ -29,32 +23,31 @@ def app
   end
 
   it "handles reuse of the env instance" do
-    env = { "HTTP_ACCEPT_LANGUAGE" => "en" }
+    env = {"HTTP_ACCEPT_LANGUAGE" => "en"}
     app = lambda { |env| env }
     middleware = HttpAcceptLanguage::Middleware.new(app)
     middleware.call(env)
-    expect(env.http_accept_language.user_preferred_languages).to eq %w{en}
+    expect(env.http_accept_language.user_preferred_languages).to eq %w[en]
     env["HTTP_ACCEPT_LANGUAGE"] = "de"
     middleware.call(env)
-    expect(env.http_accept_language.user_preferred_languages).to eq %w{de}
+    expect(env.http_accept_language.user_preferred_languages).to eq %w[de]
   end
 
   it "decodes the HTTP_ACCEPT_LANGUAGE header" do
-    request_with_header 'en-us,en-gb;q=0.8,en;q=0.6,es-419'
-    expect(r['user_preferred_languages']).to eq %w{en-US es-419 en-GB en}
+    request_with_header "en-us,en-gb;q=0.8,en;q=0.6,es-419"
+    expect(body_as_json["user_preferred_languages"]).to eq %w[en-US es-419 en-GB en]
   end
 
   it "finds the first available language" do
-    request_with_header 'en-us,en-gb;q=0.8,en;q=0.6,es-419', :preferred => %w(en en-GB)
-    expect(r['preferred_language_from']).to eq 'en-GB'
+    request_with_header "en-us,en-gb;q=0.8,en;q=0.6,es-419", preferred: %w[en en-GB]
+    expect(body_as_json["preferred_language_from"]).to eq "en-GB"
   end
 
   def request_with_header(header, params = {})
-    get "/", params, 'HTTP_ACCEPT_LANGUAGE' => header
+    get "/", params, "HTTP_ACCEPT_LANGUAGE" => header
   end
 
-  def r
+  def body_as_json
     JSON.parse(last_response.body)
   end
-
 end
diff --git a/spec/parser_spec.rb b/spec/parser_spec.rb
index 15677e2..0ed638c 100644
--- a/spec/parser_spec.rb
+++ b/spec/parser_spec.rb
@@ -1,9 +1,6 @@
-require 'http_accept_language/parser'
-
-describe HttpAcceptLanguage::Parser do
-
+RSpec.describe HttpAcceptLanguage::Parser do
   def parser
-    @parser ||= HttpAcceptLanguage::Parser.new('en-us,en-gb;q=0.8,en;q=0.6,es-419')
+    @parser ||= HttpAcceptLanguage::Parser.new("en-us,en-gb;q=0.8,en;q=0.6,es-419")
   end
 
   it "should return empty array" do
@@ -12,45 +9,45 @@ def parser
   end
 
   it "should properly split" do
-    expect(parser.user_preferred_languages).to eq %w{en-US es-419 en-GB en}
+    expect(parser.user_preferred_languages).to eq %w[en-US es-419 en-GB en]
   end
 
   it "should ignore jambled header" do
-    parser.header = 'odkhjf89fioma098jq .,.,'
+    parser.header = "odkhjf89fioma098jq .,.,"
     expect(parser.user_preferred_languages).to eq []
   end
 
   it "should properly respect whitespace" do
-    parser.header = 'en-us, en-gb; q=0.8,en;q = 0.6,es-419'
-    expect(parser.user_preferred_languages).to eq %w{en-US es-419 en-GB en}
+    parser.header = "en-us, en-gb; q=0.8,en;q = 0.6,es-419"
+    expect(parser.user_preferred_languages).to eq %w[en-US es-419 en-GB en]
   end
 
   it "should find first available language" do
-    expect(parser.preferred_language_from(%w{en en-GB})).to eq "en-GB"
+    expect(parser.preferred_language_from(%w[en en-GB])).to eq "en-GB"
   end
 
   it "should find first compatible language" do
-    expect(parser.compatible_language_from(%w{en-hk})).to eq "en-hk"
-    expect(parser.compatible_language_from(%w{en})).to eq "en"
+    expect(parser.compatible_language_from(%w[en-hk])).to eq "en-hk"
+    expect(parser.compatible_language_from(%w[en])).to eq "en"
   end
 
   it "should find first compatible from user preferred" do
-    parser.header = 'en-us,de-de'
-    expect(parser.compatible_language_from(%w{de en})).to eq 'en'
+    parser.header = "en-us,de-de"
+    expect(parser.compatible_language_from(%w[de en])).to eq "en"
   end
 
   it "should accept symbols as available languages" do
-    parser.header = 'en-us'
+    parser.header = "en-us"
     expect(parser.compatible_language_from([:"en-HK"])).to eq :"en-HK"
   end
 
   it "should accept and ignore wildcards" do
-    parser.header = 'en-US,en,*'
+    parser.header = "en-US,en,*"
     expect(parser.compatible_language_from([:"en-US"])).to eq :"en-US"
   end
 
   it "should sanitize available language names" do
-    expect(parser.sanitize_available_locales(%w{en_UK-x3 en-US-x1 ja_JP-x2 pt-BR-x5 es-419-x4})).to eq ["en-UK", "en-US", "ja-JP", "pt-BR", "es-419"]
+    expect(parser.sanitize_available_locales(%w[en_UK-x3 en-US-x1 ja_JP-x2 pt-BR-x5 es-419-x4])).to eq ["en-UK", "en-US", "ja-JP", "pt-BR", "es-419"]
   end
 
   it "should accept available language names as symbols and return them as strings" do
@@ -58,8 +55,7 @@ def parser
   end
 
   it "should find most compatible language from user preferred" do
-    parser.header = 'ja,en-gb,en-us,fr-fr'
-    expect(parser.language_region_compatible_from(%w{en-UK en-US ja-JP})).to eq "ja-JP"
+    parser.header = "ja,en-gb,en-us,fr-fr"
+    expect(parser.language_region_compatible_from(%w[en-UK en-US ja-JP])).to eq "ja-JP"
   end
-
 end
diff --git a/spec/rails_integration_spec.rb b/spec/rails_integration_spec.rb
new file mode 100644
index 0000000..7de2552
--- /dev/null
+++ b/spec/rails_integration_spec.rb
@@ -0,0 +1,19 @@
+RSpec.describe "Rails integration" do
+  describe "Controller Helper", type: :request do
+    it "returns correct language values from header" do
+      headers = {"HTTP_ACCEPT_LANGUAGE" => "en-us,en-gb;q=0.8,en;q=0.6,es-419"}
+
+      get root_path, headers: headers
+
+      expect(response.body)
+        .to include("Languages: en-US : es-419 : en-GB : en")
+    end
+  end
+
+  describe "Middleware" do
+    it "inserts middleware into the Rails application" do
+      expect(Rails.application.middleware.middlewares)
+        .to include(HttpAcceptLanguage::Middleware)
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
new file mode 100644
index 0000000..74eedce
--- /dev/null
+++ b/spec/spec_helper.rb
@@ -0,0 +1,23 @@
+if ENV.fetch("COVERAGE", false)
+  require "simplecov"
+  SimpleCov.start do
+    load_profile "test_frameworks"
+  end
+end
+
+require "action_controller/railtie"
+
+Bundler.require :default, :development
+
+Combustion.initialize! :action_controller do
+  config.load_defaults Rails::VERSION::STRING.to_f
+end
+
+require "rspec/rails"
+
+RSpec.configure do |config|
+  config.disable_monkey_patching!
+  config.example_status_persistence_file_path = ".rspec_status"
+  config.infer_spec_type_from_file_location!
+  config.use_transactional_fixtures = true
+end