diff --git a/CHANGELOG.md b/CHANGELOG.md
index 175fdac..662ecc0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 ## [Unreleased]
 
+## [0.6.0] - 2025-07-25
+
+- Add `--only` option to only include specific files or directories in the diff.
+- Add `rails-diff dotfiles` to compare dotfiles (configuration files) in the repository.
+- [BUGFIX] --fail-on-diff wasn't aborting with errors on diff.
+
 ## [0.5.0] - 2025-03-10
 
 - Don't abort process on bundle check failure.
@@ -64,6 +70,9 @@ M## [0.1.1] - 2025-02-21
 
 - Initial release
 
+[0.6.0]: https://github.com/matheusrich/rails-diff/releases/tag/v0.6.0
+[0.5.0]: https://github.com/matheusrich/rails-diff/releases/tag/v0.5.0
+[0.4.1]: https://github.com/matheusrich/rails-diff/releases/tag/v0.4.1
 [0.4.1]: https://github.com/matheusrich/rails-diff/releases/tag/v0.4.1
 [0.4.0]: https://github.com/matheusrich/rails-diff/releases/tag/v0.4.0
 [0.3.0]: https://github.com/matheusrich/rails-diff/releases/tag/v0.3.0
diff --git a/Gemfile b/Gemfile
index aa82799..e2ec273 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,6 +5,8 @@ source "https://rubygems.org/"
 # Specify your gem's dependencies in rails-diff.gemspec
 gemspec
 
+gem "simplecov", require: false
+gem "standard", "~> 1.0"
 gem "rake", "~> 13.0"
 
 gem "rspec", "~> 3.0"
diff --git a/Gemfile.lock b/Gemfile.lock
index 6cc3972..d49748b 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    rails-diff (0.5.0)
+    rails-diff (0.6.0)
       diffy (~> 3.4)
       rails (>= 7.0)
       thor (~> 1.0)
@@ -9,29 +9,29 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
-    actioncable (8.0.1)
-      actionpack (= 8.0.1)
-      activesupport (= 8.0.1)
+    actioncable (8.0.2.1)
+      actionpack (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       nio4r (~> 2.0)
       websocket-driver (>= 0.6.1)
       zeitwerk (~> 2.6)
-    actionmailbox (8.0.1)
-      actionpack (= 8.0.1)
-      activejob (= 8.0.1)
-      activerecord (= 8.0.1)
-      activestorage (= 8.0.1)
-      activesupport (= 8.0.1)
+    actionmailbox (8.0.2.1)
+      actionpack (= 8.0.2.1)
+      activejob (= 8.0.2.1)
+      activerecord (= 8.0.2.1)
+      activestorage (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       mail (>= 2.8.0)
-    actionmailer (8.0.1)
-      actionpack (= 8.0.1)
-      actionview (= 8.0.1)
-      activejob (= 8.0.1)
-      activesupport (= 8.0.1)
+    actionmailer (8.0.2.1)
+      actionpack (= 8.0.2.1)
+      actionview (= 8.0.2.1)
+      activejob (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       mail (>= 2.8.0)
       rails-dom-testing (~> 2.2)
-    actionpack (8.0.1)
-      actionview (= 8.0.1)
-      activesupport (= 8.0.1)
+    actionpack (8.0.2.1)
+      actionview (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       nokogiri (>= 1.8.5)
       rack (>= 2.2.4)
       rack-session (>= 1.0.1)
@@ -39,35 +39,35 @@ GEM
       rails-dom-testing (~> 2.2)
       rails-html-sanitizer (~> 1.6)
       useragent (~> 0.16)
-    actiontext (8.0.1)
-      actionpack (= 8.0.1)
-      activerecord (= 8.0.1)
-      activestorage (= 8.0.1)
-      activesupport (= 8.0.1)
+    actiontext (8.0.2.1)
+      actionpack (= 8.0.2.1)
+      activerecord (= 8.0.2.1)
+      activestorage (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       globalid (>= 0.6.0)
       nokogiri (>= 1.8.5)
-    actionview (8.0.1)
-      activesupport (= 8.0.1)
+    actionview (8.0.2.1)
+      activesupport (= 8.0.2.1)
       builder (~> 3.1)
       erubi (~> 1.11)
       rails-dom-testing (~> 2.2)
       rails-html-sanitizer (~> 1.6)
-    activejob (8.0.1)
-      activesupport (= 8.0.1)
+    activejob (8.0.2.1)
+      activesupport (= 8.0.2.1)
       globalid (>= 0.3.6)
-    activemodel (8.0.1)
-      activesupport (= 8.0.1)
-    activerecord (8.0.1)
-      activemodel (= 8.0.1)
-      activesupport (= 8.0.1)
+    activemodel (8.0.2.1)
+      activesupport (= 8.0.2.1)
+    activerecord (8.0.2.1)
+      activemodel (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       timeout (>= 0.4.0)
-    activestorage (8.0.1)
-      actionpack (= 8.0.1)
-      activejob (= 8.0.1)
-      activerecord (= 8.0.1)
-      activesupport (= 8.0.1)
+    activestorage (8.0.2.1)
+      actionpack (= 8.0.2.1)
+      activejob (= 8.0.2.1)
+      activerecord (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       marcel (~> 1.0)
-    activesupport (8.0.1)
+    activesupport (8.0.2.1)
       base64
       benchmark (>= 0.3)
       bigdecimal
@@ -80,17 +80,19 @@ GEM
       securerandom (>= 0.3)
       tzinfo (~> 2.0, >= 2.0.5)
       uri (>= 0.13.1)
-    base64 (0.2.0)
-    benchmark (0.4.0)
-    bigdecimal (3.1.9)
+    ast (2.4.3)
+    base64 (0.3.0)
+    benchmark (0.4.1)
+    bigdecimal (3.2.2)
     builder (3.3.0)
     concurrent-ruby (1.3.5)
-    connection_pool (2.5.0)
+    connection_pool (2.5.3)
     crass (1.0.6)
     date (3.4.1)
     diff-lcs (1.5.1)
     diffy (3.4.3)
-    drb (2.2.1)
+    docile (1.4.1)
+    drb (2.2.3)
     erubi (1.13.1)
     globalid (1.2.1)
       activesupport (>= 6.1)
@@ -101,7 +103,10 @@ GEM
       pp (>= 0.6.0)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
-    logger (1.6.6)
+    json (2.12.2)
+    language_server-protocol (3.17.0.5)
+    lint_roller (1.1.0)
+    logger (1.7.0)
     loofah (2.24.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.12.0)
@@ -112,8 +117,8 @@ GEM
       net-smtp
     marcel (1.0.4)
     mini_mime (1.1.5)
-    mini_portile2 (2.8.8)
-    minitest (5.25.4)
+    mini_portile2 (2.8.9)
+    minitest (5.25.5)
     net-imap (0.5.7)
       date
       net-protocol
@@ -124,19 +129,24 @@ GEM
     net-smtp (0.5.1)
       net-protocol
     nio4r (2.7.4)
-    nokogiri (1.18.8)
+    nokogiri (1.18.9)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
-    nokogiri (1.18.8-x86_64-darwin)
+    nokogiri (1.18.9-x86_64-darwin)
       racc (~> 1.4)
+    parallel (1.27.0)
+    parser (3.3.8.0)
+      ast (~> 2.4.1)
+      racc
     pp (0.6.2)
       prettyprint
     prettyprint (0.2.0)
+    prism (1.4.0)
     psych (5.2.3)
       date
       stringio
     racc (1.8.1)
-    rack (3.1.16)
+    rack (3.1.18)
     rack-session (2.1.1)
       base64 (>= 0.1.0)
       rack (>= 3.0.0)
@@ -144,20 +154,20 @@ GEM
       rack (>= 1.3)
     rackup (2.2.1)
       rack (>= 3)
-    rails (8.0.1)
-      actioncable (= 8.0.1)
-      actionmailbox (= 8.0.1)
-      actionmailer (= 8.0.1)
-      actionpack (= 8.0.1)
-      actiontext (= 8.0.1)
-      actionview (= 8.0.1)
-      activejob (= 8.0.1)
-      activemodel (= 8.0.1)
-      activerecord (= 8.0.1)
-      activestorage (= 8.0.1)
-      activesupport (= 8.0.1)
+    rails (8.0.2.1)
+      actioncable (= 8.0.2.1)
+      actionmailbox (= 8.0.2.1)
+      actionmailer (= 8.0.2.1)
+      actionpack (= 8.0.2.1)
+      actiontext (= 8.0.2.1)
+      actionview (= 8.0.2.1)
+      activejob (= 8.0.2.1)
+      activemodel (= 8.0.2.1)
+      activerecord (= 8.0.2.1)
+      activestorage (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       bundler (>= 1.15.0)
-      railties (= 8.0.1)
+      railties (= 8.0.2.1)
     rails-dom-testing (2.2.0)
       activesupport (>= 5.0.0)
       minitest
@@ -165,17 +175,19 @@ GEM
     rails-html-sanitizer (1.6.2)
       loofah (~> 2.21)
       nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
-    railties (8.0.1)
-      actionpack (= 8.0.1)
-      activesupport (= 8.0.1)
+    railties (8.0.2.1)
+      actionpack (= 8.0.2.1)
+      activesupport (= 8.0.2.1)
       irb (~> 1.13)
       rackup (>= 1.0.0)
       rake (>= 12.2)
       thor (~> 1.0, >= 1.2.2)
       zeitwerk (~> 2.6)
+    rainbow (3.1.1)
     rake (13.2.1)
     rdoc (6.12.0)
       psych (>= 4.0.0)
+    regexp_parser (2.10.0)
     reline (0.6.0)
       io-console (~> 0.5)
     rspec (3.13.0)
@@ -191,12 +203,52 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.13.0)
     rspec-support (3.13.2)
+    rubocop (1.75.8)
+      json (~> 2.3)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.1.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 2.9.3, < 3.0)
+      rubocop-ast (>= 1.44.0, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 4.0)
+    rubocop-ast (1.45.1)
+      parser (>= 3.3.7.2)
+      prism (~> 1.4)
+    rubocop-performance (1.25.0)
+      lint_roller (~> 1.1)
+      rubocop (>= 1.75.0, < 2.0)
+      rubocop-ast (>= 1.38.0, < 2.0)
+    ruby-progressbar (1.13.0)
     securerandom (0.4.1)
+    simplecov (0.22.0)
+      docile (~> 1.1)
+      simplecov-html (~> 0.11)
+      simplecov_json_formatter (~> 0.1)
+    simplecov-html (0.13.1)
+    simplecov_json_formatter (0.1.4)
+    standard (1.50.0)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.75.5)
+      standard-custom (~> 1.0.0)
+      standard-performance (~> 1.8)
+    standard-custom (1.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.50)
+    standard-performance (1.8.0)
+      lint_roller (~> 1.1)
+      rubocop-performance (~> 1.25.0)
     stringio (3.1.4)
-    thor (1.3.2)
+    thor (1.4.0)
     timeout (0.4.3)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
+    unicode-display_width (3.1.4)
+      unicode-emoji (~> 4.0, >= 4.0.4)
+    unicode-emoji (4.0.4)
     uri (1.0.3)
     useragent (0.16.11)
     websocket-driver (0.7.7)
@@ -213,6 +265,8 @@ DEPENDENCIES
   rails-diff!
   rake (~> 13.0)
   rspec (~> 3.0)
+  simplecov
+  standard (~> 1.0)
 
 BUNDLED WITH
    2.6.2
diff --git a/README.md b/README.md
index 5e0ac88..9deb309 100644
--- a/README.md
+++ b/README.md
@@ -67,7 +67,14 @@ rails-diff generated scaffold Post --fail-on-diff
 rails-diff generated authentication --commit 7df1b8
 ```
 
-### Options
+### Compare dotfiles (configuration files)
+
+```bash
+# Compare configuration files like .gitignore, .rspec, .rubocop.yml
+rails-diff dotfiles
+```
+
+### Global Options
 
 #### --fail-on-diff
 
@@ -96,6 +103,14 @@ Skip specific files or directories during the diff.
 rails-diff generated scaffold Post --skip app/views app/helpers
 ```
 
+#### --only <files/directories>
+
+Only include specific files or directories in the diff.
+
+```bash
+rails-diff generated scaffold Post --only app/models app/controllers
+```
+
 #### --clear-cache/--no-cache
 
 Clear the cache directory to force cloning Rails and regenerating the Rails template app.
diff --git a/lib/rails/diff.rb b/lib/rails/diff.rb
index 03d33f9..14fbc25 100644
--- a/lib/rails/diff.rb
+++ b/lib/rails/diff.rb
@@ -1,130 +1,64 @@
 # frozen_string_literal: true
 
-require_relative "diff/version"
-require_relative "diff/file_tracker"
 require "rails"
-require "thor"
 require "diffy"
 require "fileutils"
 require "open3"
+require_relative "diff/cli"
+require_relative "diff/file_tracker"
+require_relative "diff/logger"
+require_relative "diff/rails_app_generator"
+require_relative "diff/rails_repo"
+require_relative "diff/version"
 
 module Rails
   module Diff
-    class Error < StandardError; end
-
-    RAILS_REPO = "https://github.com/rails/rails.git"
     CACHE_DIR = File.expand_path("#{ENV["HOME"]}/.rails-diff/cache")
-    RAILSRC_PATH = "#{ENV["HOME"]}/.railsrc"
 
     class << self
       def file(*files, no_cache: false, commit: nil, new_app_options: nil)
-        clear_cache if no_cache
-        ensure_template_app_exists(commit, new_app_options)
+        app_generator = RailsAppGenerator.new(commit:, new_app_options:, no_cache:)
+        app_generator.create_template_app
 
-        files.filter_map { |it| diff_with_header(it) }.join("\n")
+        files
+          .filter_map { |it| diff_with_header(it, app_generator.template_app_path) }
+          .join("\n")
       end
 
       def generated(generator_name, *args, no_cache: false, skip: [], only: [], commit: nil, new_app_options: nil)
-        clear_cache if no_cache
-        ensure_template_app_exists(commit, new_app_options)
-        install_app_dependencies
+        app_generator = RailsAppGenerator.new(commit:, new_app_options:, no_cache:)
+        app_generator.create_template_app
+        app_generator.install_app_dependencies
 
-        generated_files(generator_name, *args, skip, only)
-          .map { |it| diff_with_header(it) }
+        app_generator.run_generator(generator_name, *args, skip, only)
+          .map { |it| diff_with_header(it, app_generator.template_app_path) }
           .join("\n\n")
       end
 
-      private
-
-      def system!(*cmd, abort: true)
+      def system!(*cmd, logger:, abort: true)
         _, stderr, status = Open3.capture3(*cmd)
-
-        debug cmd.join(" ")
-
+        logger.debug(cmd.join(" "))
         if status.success?
           true
         elsif abort
-          $stderr.puts "\e[1;31mCommand failed:\e[0m #{cmd.join(' ')}"
+          logger.error("Command failed:", cmd.join(" "))
           abort stderr
         else
           false
         end
       end
 
-      def info(message)
-        puts "\e[1;34minfo:\e[0m\t#{message}"
-      end
-
-      def debug(message)
-        return unless ENV["DEBUG"]
-
-        puts "\e[1;33mdebug:\e[0m\t#{message}"
-      end
-
-      def clear_cache
-        info "Clearing cache"
-        FileUtils.rm_rf(CACHE_DIR)
-      end
-
-      def ensure_template_app_exists(commit, new_app_options)
-        FileUtils.mkdir_p(CACHE_DIR)
-        @new_app_options = new_app_options
-        @commit = commit || latest_commit
-        return if cached_app?
-
-        create_new_rails_app
-      end
-
-      def template_app_path
-        @template_app_path ||= File.join(CACHE_DIR, "rails-#{commit.first(10)}", rails_new_options_hash, app_name)
-      end
-
-      def rails_path
-        @rails_path ||= begin
-          File.join(CACHE_DIR, "rails").tap do |path|
-            unless File.exist?(path)
-              info "Cloning Rails repository"
-              system!("git", "clone", "--depth", "1", RAILS_REPO, path)
-            end
-          end
-        end
-      end
-
-      def railsrc_options
-        return @railsrc_options if defined?(@railsrc_options)
-
-        @railsrc_options = File.read(RAILSRC_PATH).lines if File.exist?(RAILSRC_PATH)
-      end
-
-      def app_name = @app_name ||= File.basename(Dir.pwd)
-
-      def generated_files(generator_name, *args, skip, only)
-        Dir.chdir(template_app_path) do
-          system!("bin/rails", "destroy", generator_name, *args)
-          info "Running generator: rails generate #{generator_name} #{args.join(' ')}"
-          FileTracker.new.track_new_files(template_app_path, skip, only) { system!("bin/rails", "generate", generator_name, *args) }
-            .map { |it| it.delete_prefix("#{template_app_path}/") }
-        end
-      end
+      private
 
-      def diff_with_header(file)
-        diff = diff_file(file)
+      def diff_with_header(file, template_app_path)
+        diff = diff_file(file, template_app_path)
         return if diff.empty?
 
         header = "#{file} diff:"
         [header, "=" * header.size, diff].join("\n")
       end
 
-      def install_app_dependencies
-        Dir.chdir(template_app_path) do
-          unless system!("bundle check", abort: false)
-            info "Installing application dependencies"
-            system!("bundle install")
-          end
-        end
-      end
-
-      def diff_file(file)
+      def diff_file(file, template_app_path)
         rails_file = File.join(template_app_path, file)
         repo_file = File.join(Dir.pwd, file)
 
@@ -135,129 +69,9 @@ def diff_file(file)
           rails_file,
           repo_file,
           context: 2,
-          source: 'files'
+          source: "files"
         ).to_s(:color).chomp
       end
-
-      def cached_app?
-        File.exist?(template_app_path) && !out_of_date_rails?
-      end
-
-      def out_of_date_rails?
-        return true unless File.exist?(rails_path)
-
-        Dir.chdir(rails_path) do
-          system!("git fetch origin main")
-          current = `git rev-parse HEAD`.strip
-          latest = `git rev-parse origin/main`.strip
-
-          if current != latest
-            FileUtils.rm_rf(rails_path)
-            return true
-          end
-        end
-
-        false
-      end
-
-      def create_new_rails_app
-        Dir.chdir(rails_path) do
-          checkout_rails
-          generate_app
-        end
-      end
-
-      def generate_app
-        Dir.chdir("railties") do
-          unless system!("bundle check", abort: false)
-            info "Installing Rails dependencies"
-            system!("bundle install")
-          end
-
-          if railsrc_options
-            info "Using default options from #{RAILSRC_PATH}:\n\t  > #{railsrc_options.join(' ')}"
-          end
-
-          info "Generating new Rails application\n\t  > #{rails_new_command.join(' ')}"
-          system!(*rails_new_command)
-        end
-      end
-
-      def checkout_rails
-        info "Checking out Rails (at commit #{commit[0..6]})"
-        system!("git", "checkout", commit)
-      end
-
-      def commit = @commit
-
-      def new_app_options = @new_app_options
-
-      def latest_commit
-        Dir.chdir(rails_path) do
-          `git rev-parse origin/main`.strip
-        end
-      end
-
-      def rails_new_command = @rails_new_command ||= [
-          "bundle",
-          "exec",
-          "rails",
-          "new",
-          template_app_path,
-          "--main",
-          "--skip-bundle",
-          "--force",
-          "--quiet",
-          *rails_new_options
-        ]
-
-      def rails_new_options = @rails_new_options ||= [*new_app_options, *railsrc_options].compact
-
-      def rails_new_options_hash = Digest::MD5.hexdigest(rails_new_options.join(" "))
-    end
-
-    class CLI < Thor
-      class_option :no_cache, type: :boolean, desc: "Clear cache before running", aliases: ["--clear-cache"]
-      class_option :fail_on_diff, type: :boolean, desc: "Fail if there are differences"
-      class_option :commit, type: :string, desc: "Compare against a specific commit"
-      class_option :new_app_options, type: :string, desc: "Options to pass to the rails new command"
-      class_option :debug, type: :boolean, desc: "Print debug information", aliases: ["-d"]
-
-      def self.exit_on_failure? = true
-
-      desc "file FILE [FILE ...]", "Compare one or more files from your repository with Rails' generated version"
-      def file(*files)
-        abort "Please provide at least one file to compare" if files.empty?
-        ENV["DEBUG"] = "true" if options[:debug]
-
-        diff = Rails::Diff.file(*files, no_cache: options[:no_cache], commit: options[:commit], new_app_options: options[:new_app_options])
-        return if diff.empty?
-
-        options[:fail] ? abort(diff) : puts(diff)
-      end
-
-      desc "generated GENERATOR [args]", "Compare files that would be created by a Rails generator"
-      option :skip, type: :array, desc: "Skip specific files or directories", aliases: ["-s"], default: []
-      option :only, type: :array, desc: "Only include specific files or directories", aliases: ["-o"], default: []
-      def generated(generator_name, *args)
-        ENV["DEBUG"] = "true" if options[:debug]
-        diff = Rails::Diff.generated(generator_name, 
-                                     *args, 
-                                     no_cache: options[:no_cache], 
-                                     skip: options[:skip], 
-                                     only: options[:only],
-                                     commit: options[:commit], 
-                                     new_app_options: options[:new_app_options])
-        return if diff.empty?
-
-        options[:fail] ? abort(diff) : puts(diff)
-      end
-
-      map %w[--version -v] => :__version
-      desc "--version, -v", "print the version"
-      def __version
-        puts VERSION
-      end
     end
   end
 end
diff --git a/lib/rails/diff/cli.rb b/lib/rails/diff/cli.rb
new file mode 100644
index 0000000..15dad58
--- /dev/null
+++ b/lib/rails/diff/cli.rb
@@ -0,0 +1,63 @@
+require "thor"
+
+module Rails
+  module Diff
+    class CLI < Thor
+      class_option :no_cache, type: :boolean, desc: "Clear cache before running", aliases: ["--clear-cache"]
+      class_option :fail_on_diff, type: :boolean, desc: "Fail if there are differences"
+      class_option :commit, type: :string, desc: "Compare against a specific commit"
+      class_option :new_app_options, type: :string, desc: "Options to pass to the rails new command"
+      class_option :debug, type: :boolean, desc: "Print debug information", aliases: ["-d"]
+
+      def self.exit_on_failure? = true
+
+      desc "file FILE [FILE ...]", "Compare one or more files from your repository with Rails' generated version"
+      def file(*files)
+        abort "Please provide at least one file to compare" if files.empty?
+        ENV["DEBUG"] = "true" if options[:debug]
+
+        diff = Rails::Diff.file(
+          *files,
+          no_cache: options[:no_cache],
+          commit: options[:commit],
+          new_app_options: options[:new_app_options]
+        )
+        return if diff.empty?
+
+        options[:fail_on_diff] ? abort(diff) : puts(diff)
+      end
+
+      desc "dotfiles", "Compare dotfiles in your repository with the ones generated by Rails"
+      def dotfiles
+        dotfiles = `git ls-files --cached --others --exclude-standard -- '.*'`.split("\n")
+
+        file(*dotfiles)
+      end
+
+      desc "generated GENERATOR [args]", "Compare files that would be created by a Rails generator"
+      option :skip, type: :array, desc: "Skip specific files or directories", aliases: ["-s"], default: []
+      option :only, type: :array, desc: "Only include specific files or directories", aliases: ["-o"], default: []
+      def generated(generator_name, *args)
+        ENV["DEBUG"] = "true" if options[:debug]
+        diff = Rails::Diff.generated(
+          generator_name,
+          *args,
+          no_cache: options[:no_cache],
+          skip: options[:skip],
+          only: options[:only],
+          commit: options[:commit],
+          new_app_options: options[:new_app_options]
+        )
+        return if diff.empty?
+
+        options[:fail_on_diff] ? abort(diff) : puts(diff)
+      end
+
+      map %w[--version -v] => :__version
+      desc "--version, -v", "print the version"
+      def __version
+        puts VERSION
+      end
+    end
+  end
+end
diff --git a/lib/rails/diff/file_tracker.rb b/lib/rails/diff/file_tracker.rb
index 8468164..cd822f8 100644
--- a/lib/rails/diff/file_tracker.rb
+++ b/lib/rails/diff/file_tracker.rb
@@ -1,29 +1,39 @@
 # frozen_string_literal: true
 
-class FileTracker
-    def track_new_files(template_app_path, skip, only = [])
-        files_before = list_files(template_app_path)
+module Rails
+  module Diff
+    class FileTracker
+      def initialize(base_dir, skip = [], only = [])
+        @base_dir = base_dir
+        @skip = skip
+        @only = only
+      end
+
+      def new_files
+        files_before = list_files(@base_dir)
         yield
-        files_after = list_files(template_app_path, skip, only)
+        files_after = list_files(@base_dir, @skip, @only)
         files_after - files_before
       end
 
       private
 
-    def list_files(dir, skip = [], only = [])
-      files = Dir.glob("#{dir}/**/*", File::FNM_DOTMATCH).reject do |it|
-        File.directory?(it) ||
-        it.start_with?("#{dir}/.git") ||
-        it.start_with?("#{dir}/tmp") ||
-        it.start_with?("#{dir}/log") ||
-        it.start_with?("#{dir}/test") ||
-        skip.any? { |s| it.start_with?("#{dir}/#{s}") }
-      end
+      def list_files(dir, skip = [], only = [])
+        files = Dir.glob("#{dir}/**/*", File::FNM_DOTMATCH).reject do |it|
+          File.directory?(it) ||
+            it.start_with?("#{dir}/.git") ||
+            it.start_with?("#{dir}/tmp") ||
+            it.start_with?("#{dir}/log") ||
+            it.start_with?("#{dir}/test") ||
+            skip.any? { |s| it.start_with?("#{dir}/#{s}") }
+        end
 
-      if only.any?
-        files.select { |it| only.any? { |o| it.start_with?("#{dir}/#{o}") } }
-      else
-        files
+        if only.any?
+          files.select { |it| only.any? { |o| it.start_with?("#{dir}/#{o}") } }
+        else
+          files
+        end
       end
     end
-  end
\ No newline at end of file
+  end
+end
diff --git a/lib/rails/diff/logger.rb b/lib/rails/diff/logger.rb
new file mode 100644
index 0000000..f2e3f54
--- /dev/null
+++ b/lib/rails/diff/logger.rb
@@ -0,0 +1,21 @@
+module Rails
+  module Diff
+    module Logger
+      extend self
+
+      def info(message)
+        puts "\e[1;34minfo:\e[0m\t#{message}"
+      end
+
+      def debug(message)
+        return unless ENV["DEBUG"]
+
+        puts "\e[1;33mdebug:\e[0m\t#{message}"
+      end
+
+      def error(label, message)
+        warn "\e[1;31m#{label}\e[0m #{message}"
+      end
+    end
+  end
+end
diff --git a/lib/rails/diff/rails_app_generator.rb b/lib/rails/diff/rails_app_generator.rb
new file mode 100644
index 0000000..a2ad3cf
--- /dev/null
+++ b/lib/rails/diff/rails_app_generator.rb
@@ -0,0 +1,95 @@
+require "digest"
+
+module Rails
+  module Diff
+    class RailsAppGenerator
+      RAILSRC_PATH = "#{ENV["HOME"]}/.railsrc"
+
+      def initialize(commit: nil, new_app_options: nil, no_cache: false, logger: Logger, cache_dir: Rails::Diff::CACHE_DIR)
+        @new_app_options = new_app_options.to_s.split
+        @rails_repo = RailsRepo.new(logger:, cache_dir:)
+        @commit = commit
+        @logger = logger
+        @cache_dir = cache_dir
+        clear_cache if no_cache
+      end
+
+      def clear_cache
+        logger.info "Clearing cache"
+        FileUtils.rm_rf(cache_dir, secure: true)
+        FileUtils.mkdir_p(cache_dir)
+      end
+
+      def create_template_app
+        return if cached_app?
+
+        create_new_rails_app
+      end
+
+      def template_app_path
+        @template_app_path ||= File.join(cache_dir, rails_cache_dir_key, rails_new_options_hash, app_name)
+      end
+
+      def install_app_dependencies
+        Dir.chdir(template_app_path) do
+          unless Rails::Diff.system!("bundle check", abort: false, logger: logger)
+            logger.info "Installing application dependencies"
+            Rails::Diff.system!("bundle install", logger: logger)
+          end
+        end
+      end
+
+      def run_generator(generator_name, *args, skip, only)
+        Dir.chdir(template_app_path) do
+          Rails::Diff.system!("bin/rails", "destroy", generator_name, *args, logger: logger)
+          logger.info "Running generator: rails generate #{generator_name} #{args.join(" ")}"
+
+          FileTracker.new(template_app_path, skip, only)
+            .new_files { Rails::Diff.system!("bin/rails", "generate", generator_name, *args, logger: logger) }
+            .map { |it| it.delete_prefix("#{template_app_path}/") }
+        end
+      end
+
+      private
+
+      attr_reader :new_app_options, :rails_repo, :logger, :cache_dir
+
+      def commit = @commit ||= rails_repo.latest_commit
+
+      def rails_cache_dir_key = "rails-#{commit.first(10)}"
+
+      def railsrc_options
+        @railsrc_options ||= File.exist?(RAILSRC_PATH) ? File.readlines(RAILSRC_PATH) : []
+      end
+
+      def app_name = @app_name ||= File.basename(Dir.pwd)
+
+      def cached_app?
+        File.exist?(template_app_path) && rails_repo.up_to_date?
+      end
+
+      def create_new_rails_app
+        checkout_rails_commit
+        generate_app
+      end
+
+      def generate_app
+        rails_repo.install_dependencies
+        if railsrc_options.any?
+          logger.info "Using default options from #{RAILSRC_PATH}:\n\t  > #{railsrc_options.join(" ")}"
+        end
+        rails_repo.new_app(template_app_path, rails_new_options)
+      end
+
+      def checkout_rails_commit = rails_repo.checkout(commit)
+
+      def rails_new_options
+        @rails_new_options ||= (new_app_options + railsrc_options).compact
+      end
+
+      def rails_new_options_hash
+        Digest::MD5.hexdigest(rails_new_options.join(" "))
+      end
+    end
+  end
+end
diff --git a/lib/rails/diff/rails_repo.rb b/lib/rails/diff/rails_repo.rb
new file mode 100644
index 0000000..8b9a480
--- /dev/null
+++ b/lib/rails/diff/rails_repo.rb
@@ -0,0 +1,88 @@
+module Rails
+  module Diff
+    class RailsRepo
+      RAILS_REPO = "https://github.com/rails/rails.git"
+
+      def initialize(logger:, cache_dir: Rails::Diff::CACHE_DIR, rails_repo: RAILS_REPO)
+        @logger = logger
+        @cache_dir = cache_dir
+        @rails_repo = rails_repo
+      end
+
+      def checkout(commit)
+        on_rails_dir do
+          logger.info "Checking out Rails (at commit #{commit[0..6]})"
+          Rails::Diff.system!("git", "checkout", commit, logger: logger)
+        end
+      end
+
+      def latest_commit
+        @latest_commit ||= on_rails_dir do
+          Rails::Diff.system!("git fetch origin main", logger: logger)
+          `git rev-parse origin/main`.strip
+        end
+      end
+
+      def up_to_date?
+        File.exist?(rails_path) && on_latest_commit?
+      end
+
+      def install_dependencies
+        within "railties" do
+          unless Rails::Diff.system!("bundle check", abort: false, logger: logger)
+            logger.info "Installing Rails dependencies"
+            Rails::Diff.system!("bundle install", logger: logger)
+          end
+        end
+      end
+
+      def new_app(name, options)
+        within "railties" do
+          command = rails_new_command(name, options)
+          logger.info "Generating new Rails application\n\t  > #{command.join(" ")}"
+          Rails::Diff.system!(*command, logger: logger)
+        end
+      end
+
+      def within(dir, &block) = on_rails_dir { Dir.chdir(dir, &block) }
+
+      private
+
+      attr_reader :logger, :cache_dir, :rails_repo
+
+      def rails_path
+        File.join(cache_dir, "rails")
+      end
+
+      def on_latest_commit?
+        if current_commit == latest_commit
+          true
+        else
+          remove_repo
+          false
+        end
+      end
+
+      def on_rails_dir(&block)
+        clone_repo unless File.exist?(rails_path)
+        Dir.chdir(rails_path, &block)
+      end
+
+      def current_commit = on_rails_dir { `git rev-parse HEAD`.strip }
+
+      def remove_repo = FileUtils.rm_rf(rails_path, secure: true)
+
+      def clone_repo
+        logger.info "Cloning Rails repository"
+        Rails::Diff.system!("git", "clone", "--depth", "1", rails_repo, rails_path, logger: logger)
+      end
+
+      def rails_new_command(name, options)
+        [
+          "bundle", "exec", "rails", "new", name,
+          "--main", "--skip-bundle", "--force", "--quiet", *options
+        ]
+      end
+    end
+  end
+end
diff --git a/lib/rails/diff/version.rb b/lib/rails/diff/version.rb
index 2e6fa4a..4da0b83 100644
--- a/lib/rails/diff/version.rb
+++ b/lib/rails/diff/version.rb
@@ -2,6 +2,6 @@
 
 module Rails
   module Diff
-    VERSION = "0.5.0"
+    VERSION = "0.6.0"
   end
 end
diff --git a/spec/integration/rails/diff/file_tracker_spec.rb b/spec/integration/rails/diff/file_tracker_spec.rb
index e513e46..8e12db8 100644
--- a/spec/integration/rails/diff/file_tracker_spec.rb
+++ b/spec/integration/rails/diff/file_tracker_spec.rb
@@ -1,77 +1,75 @@
 # frozen_string_literal: true
 
-require 'rails/diff/file_tracker'
+require "rails/diff/file_tracker"
 
-RSpec.describe FileTracker do
-  context 'integration tests' do
-    let(:temp_dir) { Dir.mktmpdir }
+RSpec.describe Rails::Diff::FileTracker do
+  let(:temp_dir) { Dir.mktmpdir }
 
-    after do
-      FileUtils.remove_entry(temp_dir)
-    end
-
-    it 'tracks newly created files' do
-      FileUtils.touch("#{temp_dir}/file1.rb")
-      file_tracker = FileTracker.new
+  after do
+    FileUtils.remove_entry(temp_dir)
+  end
 
-      new_files = file_tracker.track_new_files(temp_dir, []) do
-        FileUtils.touch("#{temp_dir}/file2.rb")
-        FileUtils.touch("#{temp_dir}/file3.rb")
-      end
+  it "tracks newly created files" do
+    FileUtils.touch("#{temp_dir}/file1.rb")
+    file_tracker = described_class.new(temp_dir)
 
-      expect(new_files).to contain_exactly("#{temp_dir}/file2.rb", "#{temp_dir}/file3.rb")
+    new_files = file_tracker.new_files do
+      FileUtils.touch("#{temp_dir}/file2.rb")
+      FileUtils.touch("#{temp_dir}/file3.rb")
     end
 
-    it 'excludes skipped files' do
-      FileUtils.touch("#{temp_dir}/file1.rb")
-      file_tracker = FileTracker.new
+    expect(new_files).to contain_exactly("#{temp_dir}/file2.rb", "#{temp_dir}/file3.rb")
+  end
 
-      new_files = file_tracker.track_new_files(temp_dir, ['file2.rb']) do
-        FileUtils.touch("#{temp_dir}/file2.rb")
-        FileUtils.touch("#{temp_dir}/file3.rb")
-      end
+  it "excludes skipped files" do
+    FileUtils.touch("#{temp_dir}/file1.rb")
+    file_tracker = described_class.new(temp_dir, ["file2.rb"])
 
-      expect(new_files).to contain_exactly("#{temp_dir}/file3.rb")
+    new_files = file_tracker.new_files do
+      FileUtils.touch("#{temp_dir}/file2.rb")
+      FileUtils.touch("#{temp_dir}/file3.rb")
     end
 
-    it 'handles files with --only option' do
-      FileUtils.touch("#{temp_dir}/file1.rb")
-      file_tracker = FileTracker.new
-      new_files = file_tracker.track_new_files(temp_dir, [], ['file2.rb']) do
-        FileUtils.touch("#{temp_dir}/file2.rb")
-        FileUtils.touch("#{temp_dir}/file3.rb")
-      end
-      expect(new_files).to contain_exactly("#{temp_dir}/file2.rb")
+    expect(new_files).to contain_exactly("#{temp_dir}/file3.rb")
+  end
+
+  it "handles files with only option" do
+    FileUtils.touch("#{temp_dir}/file1.rb")
+    file_tracker = described_class.new(temp_dir, [], ["file2.rb"])
+    new_files = file_tracker.new_files do
+      FileUtils.touch("#{temp_dir}/file2.rb")
+      FileUtils.touch("#{temp_dir}/file3.rb")
     end
+    expect(new_files).to contain_exactly("#{temp_dir}/file2.rb")
+  end
 
-    it 'ignores files in special directories' do
-      FileUtils.mkdir_p("#{temp_dir}/.git")
-      FileUtils.mkdir_p("#{temp_dir}/tmp")
-      FileUtils.mkdir_p("#{temp_dir}/log")
-      FileUtils.touch("#{temp_dir}/file1.rb")
-      file_tracker = FileTracker.new
-
-      new_files = file_tracker.track_new_files(temp_dir, []) do
-        FileUtils.touch("#{temp_dir}/.git/config")
-        FileUtils.touch("#{temp_dir}/tmp/cache")
-        FileUtils.touch("#{temp_dir}/log/development.log")
-        FileUtils.touch("#{temp_dir}/file2.rb")
-      end
-
-      expect(new_files).to contain_exactly("#{temp_dir}/file2.rb")
+  it "ignores files in special directories" do
+    FileUtils.mkdir_p("#{temp_dir}/.git")
+    FileUtils.mkdir_p("#{temp_dir}/tmp")
+    FileUtils.mkdir_p("#{temp_dir}/log")
+    FileUtils.touch("#{temp_dir}/file1.rb")
+    file_tracker = described_class.new(temp_dir)
+
+    new_files = file_tracker.new_files do
+      FileUtils.touch("#{temp_dir}/.git/config")
+      FileUtils.touch("#{temp_dir}/tmp/cache")
+      FileUtils.touch("#{temp_dir}/log/development.log")
+      FileUtils.touch("#{temp_dir}/file2.rb")
     end
 
-    it 'handles nested directories' do
-      FileUtils.touch("#{temp_dir}/file1.rb")
-      file_tracker = FileTracker.new
+    expect(new_files).to contain_exactly("#{temp_dir}/file2.rb")
+  end
 
-      new_files = file_tracker.track_new_files(temp_dir, []) do
-        FileUtils.mkdir_p("#{temp_dir}/nested/dir")
-        FileUtils.touch("#{temp_dir}/nested/file2.rb")
-        FileUtils.touch("#{temp_dir}/nested/dir/file3.rb")
-      end
+  it "handles nested directories" do
+    FileUtils.touch("#{temp_dir}/file1.rb")
+    file_tracker = described_class.new(temp_dir)
 
-      expect(new_files).to contain_exactly("#{temp_dir}/nested/file2.rb", "#{temp_dir}/nested/dir/file3.rb")
+    new_files = file_tracker.new_files do
+      FileUtils.mkdir_p("#{temp_dir}/nested/dir")
+      FileUtils.touch("#{temp_dir}/nested/file2.rb")
+      FileUtils.touch("#{temp_dir}/nested/dir/file3.rb")
     end
+
+    expect(new_files).to contain_exactly("#{temp_dir}/nested/file2.rb", "#{temp_dir}/nested/dir/file3.rb")
   end
 end
diff --git a/spec/lib/rails/diff/cli_spec.rb b/spec/lib/rails/diff/cli_spec.rb
new file mode 100644
index 0000000..c793c9a
--- /dev/null
+++ b/spec/lib/rails/diff/cli_spec.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+# require "spec_helper"
+
+RSpec.describe Rails::Diff::CLI do
+  describe "#file" do
+    context "when --fail-on-diff is not specified" do
+      it "exits successfully" do
+        allow(Rails::Diff).to receive(:file).with("some_file.rb", kind_of(Hash)).and_return("diff output")
+
+        expect {
+          described_class.start(["file", "some_file.rb"])
+        }.not_to raise_error
+      end
+    end
+
+    context "when --fail-on-diff is specified" do
+      it "exits with an error code" do
+        allow(Rails::Diff).to receive(:file).with("some_file.rb", kind_of(Hash)).and_return("diff output")
+
+        expect {
+          described_class.start(["file", "some_file.rb", "--fail-on-diff"])
+        }.to raise_error(SystemExit)
+      end
+    end
+  end
+end
diff --git a/spec/lib/rails/diff/rails_repo_spec.rb b/spec/lib/rails/diff/rails_repo_spec.rb
new file mode 100644
index 0000000..2f91a95
--- /dev/null
+++ b/spec/lib/rails/diff/rails_repo_spec.rb
@@ -0,0 +1,146 @@
+# Helper indices for commits:
+#   @git_repo.commits[0] => 'add railties dir' (initial commit)
+#   @git_repo.commits[1] => 'commit1'
+#   @git_repo.commits.last => 'commit2'
+
+require "rails/diff/rails_repo"
+require "fileutils"
+require "tmpdir"
+
+RSpec.describe Rails::Diff::RailsRepo do
+  let(:logger) { spy }
+  let(:cache_dir) { Dir.mktmpdir }
+  let(:rails_path) { File.join(cache_dir, "rails") }
+
+  before(:all) do
+    @git_repo = GitRepo.new.tap do |repo|
+      repo.add_commit("commit1")
+      repo.add_commit("commit2")
+    end
+  end
+
+  after do
+    FileUtils.rm_rf(cache_dir)
+    @git_repo.cleanup
+  end
+
+  describe "#up_to_date?" do
+    it "returns false when repo is not cloned yet" do
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      result = repo.up_to_date?
+
+      expect(result).to eq false
+    end
+
+    it "returns true when repo is on the latest commit" do
+      @git_repo.clone_at_commit(@git_repo.commits.last, rails_path)
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      result = repo.up_to_date?
+
+      expect(result).to eq true
+    end
+
+    it "returns false and removes the repo when repo is on an old commit" do
+      @git_repo.clone_at_commit(@git_repo.commits.first, rails_path)
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      result = repo.up_to_date?
+
+      expect(result).to eq false
+      expect(File.exist?(rails_path)).to eq false
+    end
+  end
+
+  describe "#latest_commit" do
+    it "returns the latest commit SHA from the remote repo" do
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      latest = repo.latest_commit
+
+      expect(latest).to eq @git_repo.commits.last
+    end
+
+    it "returns the new latest commit after a new commit is pushed" do
+      new_commit = @git_repo.add_commit("commit3")
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      latest = repo.latest_commit
+
+      expect(latest).to eq new_commit
+    end
+  end
+
+  describe "#checkout" do
+    it "checks out the given commit in the repo" do
+      @git_repo.clone_at_commit(@git_repo.commits.last, rails_path)
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      # Checkout the first file commit (not the initial railties commit)
+      repo.checkout(@git_repo.commits[1])
+
+      # Verify HEAD is now at the first file commit
+      current = Dir.chdir(rails_path) { `git rev-parse HEAD`.strip }
+      expect(current).to eq @git_repo.commits[1]
+    end
+
+    it "logs the checkout info message" do
+      @git_repo.clone_at_commit(@git_repo.commits.last, rails_path)
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      repo.checkout(@git_repo.commits[1])
+
+      expect(logger).to have_received(:info)
+        .with(/Checking out Rails \(at commit #{@git_repo.commits[1][0..6]}\)/)
+    end
+  end
+
+  describe "#install_dependencies" do
+    it "runs bundle check and bundle install if needed, and logs appropriately" do
+      @git_repo.clone_at_commit(@git_repo.commits[0], rails_path)
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      # Simulate bundle check failing, so bundle install is needed
+      allow(Rails::Diff).to receive(:system!).with("bundle check", abort: false, logger: logger).and_return(false)
+      allow(Rails::Diff).to receive(:system!).with("bundle install", logger: logger).and_return(true)
+
+      repo.install_dependencies
+
+      expect(logger).to have_received(:info).with("Installing Rails dependencies")
+      expect(Rails::Diff).to have_received(:system!).with("bundle install", logger: logger)
+    end
+
+    it "does not run bundle install if bundle check passes" do
+      @git_repo.clone_at_commit(@git_repo.commits[0], rails_path)
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      # Simulate bundle check passing
+      allow(Rails::Diff).to receive(:system!).with("bundle check", abort: false, logger: logger).and_return(true)
+
+      repo.install_dependencies
+
+      expect(logger).not_to have_received(:info).with("Installing Rails dependencies")
+    end
+  end
+
+  describe "#new_app" do
+    it "runs the rails new command with the correct arguments and logs the command" do
+      @git_repo.clone_at_commit(@git_repo.commits.last, rails_path)
+      repo = described_class.new(logger:, cache_dir:, rails_repo: @git_repo.remote_repo)
+
+      allow(Rails::Diff).to receive(:system!).and_return(true)
+      app_name = "myapp"
+      options = ["--skip-test"]
+
+      repo.new_app(app_name, options)
+
+      expected_command = [
+        "bundle", "exec", "rails", "new", app_name,
+        "--main", "--skip-bundle", "--force", "--quiet", *options
+      ]
+      expect(Rails::Diff).to have_received(:system!).with(*expected_command, logger: logger)
+      expect(logger).to have_received(:info).with(/Generating new Rails application/)
+    end
+  end
+end
diff --git a/spec/rails/diff_spec.rb b/spec/rails/diff_spec.rb
deleted file mode 100644
index 24b4d43..0000000
--- a/spec/rails/diff_spec.rb
+++ /dev/null
@@ -1,36 +0,0 @@
-# frozen_string_literal: true
-
-RSpec.describe Rails::Diff do
-  it "has a version number" do
-    expect(Rails::Diff::VERSION).not_to be nil
-  end
-  
-  describe ".generated" do
-    before do
-      allow(Rails::Diff).to receive(:system!).and_return(true)
-      allow(Rails::Diff).to receive(:ensure_template_app_exists)
-      allow(Rails::Diff).to receive(:install_app_dependencies)
-      allow(Rails::Diff).to receive(:generated_files).and_return(["file1.rb", "file2.rb"])
-      allow(Rails::Diff).to receive(:diff_with_header).and_return("file1.rb diff:\n===\nDiff content")
-    end
-
-    it "returns the diff for generated files" do
-      result = Rails::Diff.generated("model", "User", no_cache: true)
-      expect(result).to include("file1.rb diff:")
-    end
-  end
-
-  describe Rails::Diff::CLI do
-    describe "#generated" do
-      before do
-        allow(Rails::Diff).to receive(:system!).and_return(true)
-        allow(Rails::Diff).to receive(:generated).and_return("file1.rb diff:\n===\nDiff content")
-      end
-
-      it "runs without error" do
-        cli = Rails::Diff::CLI.new
-        expect { cli.generated("model", "User") }.not_to raise_error
-      end
-    end
-  end
-end
\ No newline at end of file
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 70fce95..9691d91 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,7 +1,13 @@
 # frozen_string_literal: true
 
+require "simplecov"
+SimpleCov.start do
+  enable_coverage :branch
+  add_filter "/spec/"
+end
+
 require "rails/diff"
-$LOAD_PATH.unshift(File.expand_path('../../lib', __dir__))
+Dir["./spec/support/**/*.rb"].sort.each { |f| require f }
 
 RSpec.configure do |config|
   # Enable flags like --only-failures and --next-failure
diff --git a/spec/support/git_repo.rb b/spec/support/git_repo.rb
new file mode 100644
index 0000000..89770e1
--- /dev/null
+++ b/spec/support/git_repo.rb
@@ -0,0 +1,58 @@
+require "fileutils"
+require "tmpdir"
+
+class GitRepo
+  attr_reader :remote_repo, :commits
+
+  # Initializes and creates a bare remote repo and a working repo with main branch
+  def initialize
+    @remote_dir = Dir.mktmpdir
+    @remote_repo = File.join(@remote_dir, "origin.git")
+    Dir.chdir(@remote_dir) { `git init --bare --initial-branch=main origin.git > /dev/null 2>&1` }
+
+    @commits = []
+    @work_dir = Dir.mktmpdir
+    Dir.chdir(@work_dir) do
+      `git clone #{@remote_repo} . > /dev/null 2>&1`
+      `git checkout -b main > /dev/null 2>&1`
+      FileUtils.mkdir_p("railties")
+      File.write("railties/README", "keep")
+      `git add railties > /dev/null 2>&1`
+
+      `git config user.email 'test@example.com'`
+      `git config user.name 'Test User'`
+
+      commit_result = `git commit -m "add railties dir" 2>&1`
+      raise "Initial commit failed: #{commit_result}" unless $?.success?
+      @commits << `git rev-parse HEAD`.strip
+      `git push -u origin main > /dev/null 2>&1`
+    end
+  end
+
+  def add_commit(message)
+    Dir.chdir(@work_dir) do
+      `git commit --allow-empty -n -m "#{message}" > /dev/null 2>&1`
+      sha = `git rev-parse HEAD`.strip
+      @commits << sha
+      `git push origin main > /dev/null 2>&1`
+      `git fetch origin main > /dev/null 2>&1`
+    end
+
+    @commits.last
+  end
+
+  def clone_at_commit(commit_sha, dest_path)
+    `git clone #{@remote_repo} #{dest_path} > /dev/null 2>&1`
+    Dir.chdir(dest_path) do
+      `git checkout #{commit_sha} > /dev/null 2>&1`
+      `git fetch origin main > /dev/null 2>&1`
+    end
+  end
+
+  def cleanup
+    Dir.chdir(@work_dir) do
+      `git reset --hard main > /dev/null 2>&1`
+      `git clean -fdx > /dev/null 2>&1`
+    end
+  end
+end