diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..b79ea7d
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,20 @@
+name: ubuntu
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: build (${{ matrix.ruby }} / ${{ matrix.os }})
+    strategy:
+      matrix:
+        ruby: [ '3.0', 2.7, 2.6, head ]
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@master
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+    - name: Run test
+      run: rake test
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..3b9d383
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,22 @@
+Copyright 2019-2020 Nobuyoshi Nakada, Yusuke Endoh
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
index f3b56aa..4cc0282 100644
--- a/README.md
+++ b/README.md
@@ -42,10 +42,26 @@ ruby2_keywords def oldstyle_keywords(options = {})
 end
 ```
 
+You can do the same for a method defined by `Module#define_method`:
+
+```ruby
+define_method :delegating_method do |*args, &block|
+  other_method(*args, &block)
+end
+ruby2_keywords :delegating_method
+```
+
 ## Contributing
 
-Bug reports and pull requests are welcome on GitHub at https://bugs.ruby-lang.org.
+Bug reports and pull requests are welcome on [GitHub] or
+[Ruby Issue Tracking System].
 
 ## License
 
-The gem is available as open source under the terms of the [2-Clause BSD License](https://opensource.org/licenses/BSD-2-Clause).
+The gem is available as open source under the terms of the
+[Ruby License] or the [2-Clause BSD License].
+
+[GitHub]: https://github.com/ruby/ruby2_keywords/
+[Ruby Issue Tracking System]: https://bugs.ruby-lang.org
+[Ruby License]: https://www.ruby-lang.org/en/about/license.txt
+[2-Clause BSD License]: https://opensource.org/licenses/BSD-2-Clause
diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..8830e05
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,8 @@
+require "bundler/gem_tasks"
+require "rake/testtask"
+
+Rake::TestTask.new(:test) do |t|
+  t.test_files = FileList["test/**/test_*.rb"]
+end
+
+task :default => :test
diff --git a/lib/ruby2_keywords.rb b/lib/ruby2_keywords.rb
index 8c48333..97cd081 100644
--- a/lib/ruby2_keywords.rb
+++ b/lib/ruby2_keywords.rb
@@ -1,6 +1,10 @@
 class Module
-  unless respond_to?(:ruby2_keywords, true)
+  unless private_method_defined?(:ruby2_keywords, true)
     private
+    # call-seq:
+    #    ruby2_keywords(method_name, ...)
+    #
+    # Does nothing.
     def ruby2_keywords(name, *)
       # nil
     end
@@ -9,6 +13,10 @@ def ruby2_keywords(name, *)
 
 main = TOPLEVEL_BINDING.receiver
 unless main.respond_to?(:ruby2_keywords, true)
+  # call-seq:
+  #    ruby2_keywords(method_name, ...)
+  #
+  # Does nothing.
   def main.ruby2_keywords(name, *)
     # nil
   end
@@ -16,8 +24,34 @@ def main.ruby2_keywords(name, *)
 
 class Proc
   unless method_defined?(:ruby2_keywords)
+    # call-seq:
+    #    proc.ruby2_keywords -> proc
+    #
+    # Does nothing and just returns the receiver.
     def ruby2_keywords
       self
     end
   end
 end
+
+class << Hash
+  unless method_defined?(:ruby2_keywords_hash?)
+    # call-seq:
+    #    Hash.ruby2_keywords_hash?(hash) -> false
+    #
+    # Returns false.
+    def ruby2_keywords_hash?(hash)
+      false
+    end
+  end
+
+  unless method_defined?(:ruby2_keywords_hash)
+    # call-seq:
+    #    Hash.ruby2_keywords_hash(hash) -> new_hash
+    #
+    # Duplicates a given hash and returns the new hash.
+    def ruby2_keywords_hash(hash)
+      hash.dup
+    end
+  end
+end
diff --git a/ruby2_keywords.gemspec b/ruby2_keywords.gemspec
index 623c58c..5eac57b 100644
--- a/ruby2_keywords.gemspec
+++ b/ruby2_keywords.gemspec
@@ -1,16 +1,18 @@
-version = IO.popen(%W[git -C #{__dir__} describe --tags --match v[0-9]*], &:read)[/\Av?(\d+(?:\.\d+)*)/, 1]
+version = "0.0.3"
+abort "Version must not reach 1" if version[/\d+/].to_i >= 1
 
 Gem::Specification.new do |s|
   s.name = "ruby2_keywords"
   s.version = version
   s.summary = "Shim library for Module#ruby2_keywords"
   s.homepage = "https://github.com/ruby/ruby2_keywords"
-  s.licenses = ["Ruby"]
+  s.licenses = ["Ruby", "BSD-2-Clause"]
   s.authors = ["Nobuyoshi Nakada"]
   s.require_paths = ["lib"]
+  s.rdoc_options = ["--main", "README.md"]
   s.files = [
+    "LICENSE",
     "README.md",
     "lib/ruby2_keywords.rb",
-    "ruby2_keywords.gemspec",
   ]
 end
diff --git a/test/test_keyword.rb b/test/test_keyword.rb
new file mode 100644
index 0000000..5fcecb5
--- /dev/null
+++ b/test/test_keyword.rb
@@ -0,0 +1,41 @@
+require 'test/unit'
+LOADING_RUBY2_KEYWORDS = (RUBY_VERSION.scan(/\d+/).map(&:to_i) <=> [2, 7]) < 0
+if LOADING_RUBY2_KEYWORDS
+  require 'ruby2_keywords'
+end
+
+class TestKeywordArguments < Test::Unit::TestCase
+  def test_loaded_features
+    list = $LOADED_FEATURES.grep(%r[/ruby2_keywords\.rb\z])
+    if LOADING_RUBY2_KEYWORDS
+      assert_not_empty(list)
+      assert_not_include($LOADED_FEATURES, "ruby2_keywords.rb")
+    else
+      assert_empty(list)
+      assert_include($LOADED_FEATURES, "ruby2_keywords.rb")
+    end
+  end
+
+  def test_module_ruby2_keywords
+    assert_send([Module, :private_method_defined?, :ruby2_keywords])
+    assert_operator(Module.instance_method(:ruby2_keywords).arity, :<, 0)
+  end
+
+  def test_toplevel_ruby2_keywords
+    main = TOPLEVEL_BINDING.receiver
+    assert_send([main, :respond_to?, :ruby2_keywords, true])
+    assert_operator(main.method(:ruby2_keywords).arity, :<, 0)
+  end
+
+  def test_proc_ruby2_keywords
+    assert_respond_to(Proc.new {}, :ruby2_keywords)
+  end
+
+  def test_hash_ruby2_keywords_hash?
+    assert_false(Hash.ruby2_keywords_hash?({}))
+  end
+
+  def test_hash_ruby2_keywords_hash
+    assert_equal({}, Hash.ruby2_keywords_hash({}.freeze))
+  end
+end