Use test-unit-ruby-core gem (#51)

Author: hsbt

Gemfile

@@ -6,4 +6,5 @@ group :development do
   gem 'rake'
   gem 'rake-compiler'
   gem 'test-unit'
+  gem "test-unit-ruby-core"
 end

Rakefile

@@ -16,11 +16,4 @@ else
   task test: :compile
 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