diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 084b5f4f..d06c8114 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,6 +10,7 @@ jobs:
         os: [ubuntu-latest]
         ruby-version:
           - head
+          - '4.0'
           - '3.4'
           - '3.3'
           - '3.2'
diff --git a/.rubocop.yml b/.rubocop.yml
index 3db15b9d..55fddef2 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -4,7 +4,7 @@
 # https://github.com/bbatsov/rubocop/tree/master/config
 
 AllCops:
-  TargetRubyVersion: 3.4
+  TargetRubyVersion: 4.0
   NewCops: enable
 
 # General
diff --git a/Changelog.md b/Changelog.md
index e61950fa..ec1ab9ef 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -3,6 +3,7 @@
 Below is a complete listing of changes for each revision of HighLine.
 
 ### 3.1.2 / 2025-01-05
+* Fix Ruby software license URL in LICENSE file (@jeffwidman)
 * PR #279 - Upgrades and adjustments for Ruby 3.4 release (@abinoam)
 * PR #278 - Prevent ArgumentError for #col_count_calculate when items exceed 80 chars (@davidjkling, @justintsteele)
 
diff --git a/Gemfile b/Gemfile
index 2c9d8e4c..cdd812fa 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,7 +13,7 @@ group :code_quality do
   gem "flog", require: false
   gem "pronto", require: false, platform: :ruby
   gem "pronto-flay", require: false, platform: :ruby
-  gem "path_expander", "1.1.1", require: false # Remove this lock when path_expander > 1.1.2 and flay > 2.13.3 is released.
+  gem "path_expander", require: false
   # gem "pronto-poper", require: false, platform: :ruby
   gem "pronto-reek", require: false, platform: :ruby
   gem "pronto-rubocop", require: false, platform: :ruby
diff --git a/TODO b/TODO
deleted file mode 100644
index 89c5306e..00000000
--- a/TODO
+++ /dev/null
@@ -1,6 +0,0 @@
-= To Do List
-
-The following is a list of planned expansions for HighLine, in no particular
-order.
-
-* Rent this space.
diff --git a/doc/.cvsignore b/doc/.cvsignore
deleted file mode 100644
index 1936cc1d..00000000
--- a/doc/.cvsignore
+++ /dev/null
@@ -1 +0,0 @@
-html
diff --git a/test/Dockerfile b/test/Dockerfile
index 70b9d256..9301eb7b 100644
--- a/test/Dockerfile
+++ b/test/Dockerfile
@@ -1,11 +1,11 @@
-FROM ruby
+FROM ruby:latest
 
 WORKDIR /highline
 
 
 RUN bash -ec 'apt update; apt -y install cmake'
 
-ADD Gemfile highline.gemspec .git* ./
+ADD Gemfile Gemfile.lock highline.gemspec .git* ./
 ADD lib/highline/version.rb ./lib/highline/version.rb
 RUN bundle install
 
diff --git a/test/test_string_extension.rb b/test/test_string_extension.rb
index d9c02385..2963bc6f 100644
--- a/test/test_string_extension.rb
+++ b/test/test_string_extension.rb
@@ -66,12 +66,19 @@ def test_highline_string_still_raises_for_non_available_messages
   end
 
   def test_String_includes_StringExtension_when_receives_colorize_strings
-    @include_received = 0
-    caller = proc { @include_received += 1 }
-    ::String.stub :include, caller do
+    include_received = 0
+    ::String.singleton_class.define_method(:include) do |*modules|
+      include_received += 1
+      modules
+    end
+
+    begin
       HighLine.colorize_strings
+    ensure
+      ::String.singleton_class.remove_method(:include)
     end
-    assert_equal 1, @include_received
+
+    assert_equal 1, include_received
   end
 
   def test_respond_to_dynamic_style_methods