diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..41f80ea
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,21 @@
+name: test
+
+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 ]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - name: Run test
+      run: bundle exec rake test
diff --git a/Gemfile b/Gemfile
index c92243f..eb86192 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,8 +1,4 @@
 source "https://rubygems.org"
 
-gemspec
-
-group :development do
-  gem "bundler"
-  gem "rake"
-end
+gem "rake"
+gem "test-unit"
diff --git a/test/test_getoptlong.rb b/test/test_getoptlong.rb
index 2d496e6..0cd370b 100644
--- a/test/test_getoptlong.rb
+++ b/test/test_getoptlong.rb
@@ -20,7 +20,7 @@ def verify(test_argv, expected_remaining_argv, expected_options)
       actual_options << "#{opt}: #{arg}"
     end
     # Save remaining test ARGV and restore original ARGV.
-    actual_remaining_argv = ARGV
+    actual_remaining_argv = ARGV.dup
     ARGV.replace(argv_saved)
     # Assert.
     assert_equal(expected_remaining_argv, actual_remaining_argv, 'ARGV')