Use test-unit-ruby-core gem

.github/workflows/test.yml

@@ -28,4 +28,4 @@ jobs:
     - name: Install dependencies
       run: bundle install
     - name: Run test
-      run: rake test
+      run: bundle exec rake test

Gemfile

@@ -4,4 +4,5 @@ group :development do
   gem "bundler"
   gem "rake"
   gem "test-unit"
+  gem "test-unit-ruby-core"
 end

Rakefile

@@ -7,11 +7,4 @@ Rake::TestTask.new(:test) do |t|
   t.test_files = FileList['test/**/test_*.rb']
 end
 
-task :sync_tool do
-  require 'fileutils'
-  FileUtils.cp "../ruby/tool/lib/core_assertions.rb", "./test/lib"
-  FileUtils.cp "../ruby/tool/lib/envutil.rb", "./test/lib"
-  FileUtils.cp "../ruby/tool/lib/find_executable.rb", "./test/lib"
-end
-
 task :default => :test