test_io.rb: test for write
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40894 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_io.rb: test for write
for write part. [ruby-core:55098] [Bug #8431]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40894 b2dd03c8-39d4-4d8f-98ff-823fe69b080e