diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index 7226b7a..9762ab3 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -1,30 +1,44 @@
-name: Ruby CI
+name: Development
 
-on:
-  push:
-    branches: [ master ]
-  pull_request:
-    branches: [ master ]
+on: [push, pull_request]
 
 jobs:
   test:
-
-    name: Ruby ${{ matrix.ruby-version }} ${{ matrix.os }}
-    runs-on: ${{ matrix.os }}
+    runs-on: ${{matrix.os}}-latest
+    continue-on-error: ${{matrix.experimental}}
+    
     strategy:
-      fail-fast: false
       matrix:
-        os: [ubuntu-latest]
-        ruby-version: ['2.6', '2.7', '3.0']
-
+        os:
+          - ubuntu
+          - macos
+        
+        ruby:
+          - "2.6"
+          - "2.7"
+          - "3.0"
+        
+        experimental: [false]
+        env: [""]
+        
+        include:
+          - os: ubuntu
+            ruby: truffleruby
+            experimental: true
+          - os: ubuntu
+            ruby: jruby
+            experimental: true
+          - os: ubuntu
+            ruby: head
+            experimental: true
+    
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Ruby
-      uses: ruby/setup-ruby@v1
+    - uses: ruby/setup-ruby@v1
       with:
-        ruby-version: ${{ matrix.ruby-version }}
-        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+        ruby-version: ${{matrix.ruby}}
+        bundler-cache: true
+    
     - name: Run tests
-      run: bundle exec rake
-      env:
-        RUBYOPT: --enable-frozen-string-literal
+      timeout-minutes: 5
+      run: ${{matrix.env}} bundle exec rspec
diff --git a/Gemfile b/Gemfile
index 0c1a000..aef3a75 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 gemspec
 
diff --git a/Rakefile b/Rakefile
index f5cbbfd..366c7f8 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "bundler/gem_tasks"
 require "rspec/core/rake_task"
 
diff --git a/lib/multipart.rb b/lib/multipart.rb
index 63bbf6e..c3f88ab 100644
--- a/lib/multipart.rb
+++ b/lib/multipart.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #--
 # Copyright (c) 2007-2013 Nick Sieger.
 # See the file README.txt included with the distribution for
diff --git a/lib/multipart/post.rb b/lib/multipart/post.rb
index f726be1..c23691c 100644
--- a/lib/multipart/post.rb
+++ b/lib/multipart/post.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Multipart
   module Post
   end
diff --git a/lib/multipart/post/composite_read_io.rb b/lib/multipart/post/composite_read_io.rb
index 56ef5db..b958959 100644
--- a/lib/multipart/post/composite_read_io.rb
+++ b/lib/multipart/post/composite_read_io.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #--
 # Copyright (c) 2007-2012 Nick Sieger.
 # See the file README.txt included with the distribution for
diff --git a/lib/multipart/post/multipartable.rb b/lib/multipart/post/multipartable.rb
index 27ba8ed..ed4cdd8 100644
--- a/lib/multipart/post/multipartable.rb
+++ b/lib/multipart/post/multipartable.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #--
 # Copyright (c) 2007-2013 Nick Sieger.
 # See the file README.txt included with the distribution for
diff --git a/lib/multipart/post/parts.rb b/lib/multipart/post/parts.rb
index 7ce5724..0b352eb 100644
--- a/lib/multipart/post/parts.rb
+++ b/lib/multipart/post/parts.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #--
 # Copyright (c) 2007-2013 Nick Sieger.
 # See the file README.txt included with the distribution for
diff --git a/lib/multipart/post/version.rb b/lib/multipart/post/version.rb
index cb5120c..90c11fd 100644
--- a/lib/multipart/post/version.rb
+++ b/lib/multipart/post/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Multipart
   module Post
     VERSION = "2.1.1"
diff --git a/lib/net/http/post/multipart.rb b/lib/net/http/post/multipart.rb
index ac56097..ca80323 100644
--- a/lib/net/http/post/multipart.rb
+++ b/lib/net/http/post/multipart.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #--
 # Copyright (c) 2007-2012 Nick Sieger.
 # See the file README.txt included with the distribution for
diff --git a/multipart-post.gemspec b/multipart-post.gemspec
index ef5fed1..36ea033 100644
--- a/multipart-post.gemspec
+++ b/multipart-post.gemspec
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # -*- encoding: utf-8 -*-
 $:.push File.expand_path("../lib", __FILE__)
 require "multipart/post/version"
diff --git a/spec/multipart/post/composite_read_io_spec.rb b/spec/multipart/post/composite_read_io_spec.rb
index 5f2f23f..5517ced 100644
--- a/spec/multipart/post/composite_read_io_spec.rb
+++ b/spec/multipart/post/composite_read_io_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright, 2012, by Nick Sieger.
 # Copyright, 2017, by Samuel G. D. Williams. <http://www.codeotaku.com>
 # 
diff --git a/spec/multipart/post/parts_spec.rb b/spec/multipart/post/parts_spec.rb
index 5c5d286..4b32a1d 100644
--- a/spec/multipart/post/parts_spec.rb
+++ b/spec/multipart/post/parts_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright, 2012, by Nick Sieger.
 # Copyright, 2017, by Samuel G. D. Williams. <http://www.codeotaku.com>
 #
diff --git a/spec/net/http/post/multipart_spec.rb b/spec/net/http/post/multipart_spec.rb
index 3d6002e..679487d 100644
--- a/spec/net/http/post/multipart_spec.rb
+++ b/spec/net/http/post/multipart_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #--
 # Copyright (c) 2007-2013 Nick Sieger.
 # See the file README.txt included with the distribution for
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 6082995..38e245c 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 
 if ENV['COVERAGE']
 	begin