diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
new file mode 100644
index 0000000..a2e8532
--- /dev/null
+++ b/.github/workflows/main.yml
@@ -0,0 +1,52 @@
+name: Ruby
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+        # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
+        ruby: [2.3, 2.4, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3, 3.4, '4.0']
+        exclude:
+          - os: windows-latest
+            ruby: 2.3
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - uses: actions/checkout@v6
+    - name: before_setup
+      shell: bash
+      run: |
+        case ${{ matrix.os }} in
+        ubuntu-latest)
+          sudo apt-get update && sudo apt-get install -yq libfftw3-dev
+          ;;
+        windows-latest)
+          vcpkg install fftw3 --triplet=x64-mingw-static
+          # find $(cygpath -u "$VCPKG_INSTALLATION_ROOT")/packages -name "*fftw3*"
+          echo "BUNDLE_BUILD__NUMO___FFTW=\"--with-fftw-dir=$(cygpath -m ${VCPKG_INSTALLATION_ROOT})/packages/fftw3_x64-mingw-static\"" >> $GITHUB_ENV
+          ;;
+        esac
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      id: ruby-inst
+      env:
+        BUNDLE_BUILD__NUMO___NARRAY: --with-cflags=-std=c17
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - name: Run the default task
+      run: |
+        bundle exec rake compile -- ${{ env.BUNDLE_BUILD__NUMO___FFTW }}
+        bundle exec rake spec
+    - name: Upload artifact for error reproduction when failure
+      if: ${{ failure() }}
+      uses: actions/upload-artifact@v7
+      with:
+        name: gem-build-logs.${{ matrix.os }}_${{ matrix.ruby }}
+        path: |
+          ${{ github.workspace }}/vendor/bundle/ruby/**/gems/
+          ${{ github.workspace }}/vendor/bundle/ruby/**/mkmf.log
\ No newline at end of file
diff --git a/.rspec b/.rspec
new file mode 100644
index 0000000..34c5164
--- /dev/null
+++ b/.rspec
@@ -0,0 +1,3 @@
+--format documentation
+--color
+--require spec_helper
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..2e7431b
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+# Specify your gem's dependencies in gps_pvt.gemspec
+gemspec
diff --git a/Rakefile b/Rakefile
index 8fd75b9..edee9bb 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,13 +1,21 @@
 require "bundler/gem_tasks"
 
-task :doc do
-  dir = "ext/numo/fftw"
-  src = %w[fftw.c]
-  path = src.map{|s| File.join(dir,s)}
-  sh "cd #{dir}; ruby extconf.rb; make #{src.join(' ')}"
-  sh "rm -rf yard .yardoc; yard doc -o yard -m markdown -r README.md #{path.join(' ')}"
+require "rspec/core/rake_task"
+RSpec::Core::RakeTask.new(:spec)
+
+require "rake/extensiontask"
+Rake::ExtensionTask.new("numo/fftw") do |ext|
+  ext.lib_dir = "lib/numo"
 end
 
-task :cleandoc do
-  rm_rf %w[yard .yardoc]
+require "yard"
+YARD::Rake::YardocTask.new do |t|
+  t.before = proc{
+    Rake::Task["compile:numo/fftw"].invoke
+  }
+  t.files = Dir['**/numo/fftw/**/fftw.c', __dir__]
+  t.options = ['--embed-mixins']
+  #t.stats_options = ['--list-undoc']
 end
+
+task :default => [:compile, :spec]
diff --git a/ext/numo/fftw/depend b/ext/numo/fftw/depend
index decf83a..6e08e58 100644
--- a/ext/numo/fftw/depend
+++ b/ext/numo/fftw/depend
@@ -2,13 +2,4 @@ CLEANOBJS = *.o */*.o *.bak *~
 ERB = erb -T-
 
 fftw.c: fftw.erb.c
-	$(ERB) fftw.erb.c > fftw.c
-
-doc : fftw.c
-	yard doc -o yard -m markdown $<
-
-clean: cleansrc cleandoc
-cleansrc:
-	-$(Q)$(RM) fftw.c
-cleandoc:
-	-$(Q)$(RM_RF) yard .yardoc
+	$(ERB) $^ > $@
\ No newline at end of file
diff --git a/ext/numo/fftw/fftw.erb.c b/ext/numo/fftw/fftw.erb.c
index 209f9fe..89a10ba 100644
--- a/ext/numo/fftw/fftw.erb.c
+++ b/ext/numo/fftw/fftw.erb.c
@@ -150,10 +150,10 @@ numo_fftw_<%=func%>(VALUE mod, VALUE vna, VALUE vsign)
 void
 Init_fftw()
 {
-    VALUE mNumo,mFFTW;
+    VALUE /*mNumo,*/ mFFTW; // CAUTION: mNumo is already defined in narray.h
 
-    rb_require("numo/narray");
-    mNumo = rb_define_module("Numo");
+    //rb_require("numo/narray"); // move to fftw.rb because numo/narray.so should be loaded before Init_fftw()
+    //mNumo = rb_define_module("Numo");
     mFFTW = rb_define_module_under(mNumo,"FFTW");
 
 <% $funcs.each do |f| %>
diff --git a/lib/numo/fftw.rb b/lib/numo/fftw.rb
new file mode 100644
index 0000000..6d3e55d
--- /dev/null
+++ b/lib/numo/fftw.rb
@@ -0,0 +1,2 @@
+require "numo/narray"
+require "numo/fftw.#{RbConfig::CONFIG['DLEXT']}"
diff --git a/numo-fftw.gemspec b/numo-fftw.gemspec
index efa3586..4dbb4ef 100644
--- a/numo-fftw.gemspec
+++ b/numo-fftw.gemspec
@@ -27,7 +27,10 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.extensions    = ["ext/numo/fftw/extconf.rb"]
 
-  spec.add_development_dependency "bundler", "~> 1.3"
-  spec.add_development_dependency "rake", "~> 0"
+  spec.add_development_dependency "bundler", ">= 1.3"
+  spec.add_development_dependency "rake"
+  spec.add_development_dependency "rake-compiler"
+  spec.add_development_dependency "rspec"
+  spec.add_development_dependency "yard"
   spec.add_runtime_dependency "numo-narray", ">= 0.9.0.8"
 end
diff --git a/spec/complexFFT_spec.rb b/spec/complexFFT_spec.rb
new file mode 100644
index 0000000..3edab94
--- /dev/null
+++ b/spec/complexFFT_spec.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+# port from numru-fftw3/test/complexFFT.rb
+
+require 'rspec'
+
+require "numo/fftw"
+
+module Numo::FFTW
+  FORWARD = -1
+  BACKWARD = 1
+  singleton_methods.each{|func|
+    slice = (/(\d)d/ =~ func.to_s) ? $1.to_i : 0
+    {:fw => FORWARD, :bk => BACKWARD}.each{|dir, sign|
+      define_singleton_method("#{func}_#{dir}".to_sym){|na|
+        res = send(func, na, sign)
+        (dir == :bk) ? (res / res.shape[-slice..-1].inject(:*)) : res
+      }
+    }
+  }
+end
+
+RSpec::describe Numo::FFTW do
+  let(:fftw){described_class}
+  let(:eps){1e-10}
+  let(:seps){1e-6}
+  
+  it 'can perform forward and backward FFT' do # test_fft_fw_bk
+    na = Numo::DFloat::new(8,4).fill(1)  # will be corced to complex
+    na[1,1]=5
+    fc = fftw.dft_fw(na)
+    nb = fftw.dft_bk(fc).real
+    expect((na-nb).abs.max).to be < eps
+
+    fc = fftw.dft_1d_fw(na)
+    nb = fftw.dft_1d_bk(fc).real
+    expect((na-nb).abs.max).to be < eps
+  end
+  
+  it 'can perform real forward FFT' do # test_real_all_dims
+    na = Numo::DFloat::new(8,4).fill(1)  # will be corced to complex
+    na[1,1]=5
+    fc = fftw.dft(na, fftw::FORWARD)/na.length 
+    nb = fftw.dft(fc, fftw::BACKWARD).real
+    expect((na-nb).abs.max).to be < eps
+  end
+
+  it 'can perform complex forward FFT' do # test_complex_all_dims
+    na = Numo::DComplex::new(8,4).fill(1) * Complex::I
+    na[1,1]=5
+    fc = fftw.dft(na, fftw::FORWARD)/na.length 
+    nb = fftw.dft(fc, fftw::BACKWARD)
+    expect((na-nb).abs.max).to be < eps
+  end
+  
+  it 'can perform single precision forward FFT' do # test_single_float
+    # single float (treated as single if lib fftw3f exits).
+    # see http://www.fftw.org/fftw3_doc/Precision.html for more info
+    na = Numo::SFloat::new(8,4).indgen
+    fc = fftw.dft(na, fftw::FORWARD)/na.length 
+    nb = fftw.dft(fc, fftw::BACKWARD).real
+    expect((na-nb).abs.max).to be < eps
+  end
+end
+
+__END__
+# TODO:
+class FFTW3Test < Test::Unit::TestCase
+  def test_dim_selection
+    na = NArray.float(8,4).indgen!
+    fc = FFTW3.fft(na, FFTW3::FORWARD, 0)
+    fc = FFTW3.fft(fc, FFTW3::FORWARD, 1)
+    fc2 = FFTW3.fft(na, FFTW3::FORWARD)
+    assert( (fc-fc2).abs.max < @eps )
+  end
+end
+
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
new file mode 100644
index 0000000..b960d8c
--- /dev/null
+++ b/spec/spec_helper.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+RSpec.configure do |config|
+  # Enable flags like --only-failures and --next-failure
+  config.example_status_persistence_file_path = ".rspec_status"
+
+  # Disable RSpec exposing methods globally on `Module` and `main`
+  config.disable_monkey_patching!
+
+  config.expect_with :rspec do |c|
+    c.syntax = :expect
+  end
+end