Try to use ruby core test suite

Author: hsbt

Rakefile

@@ -2,9 +2,9 @@ require "bundler/gem_tasks"
 require "rake/testtask"
 
 Rake::TestTask.new(:test) do |t|
-  t.libs << "test"
-  t.libs << "lib"
-  t.test_files = FileList["test/**/*_test.rb"]
+  t.libs << "test/lib"
+  t.ruby_opts << "-rhelper"
+  t.test_files = FileList["test/**/test_*.rb"]
 end
 
 task :default => :test