test_flip.rb: flip-flop shared by threads
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38747 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_flip.rb: flip-flop shared by threads
should be separated per threads
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38747 b2dd03c8-39d4-4d8f-98ff-823fe69b080e