test_process.rb: use assert_in_out_err
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49822 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_process.rb: use assert_in_out_err
assert_in_out_err to simplify and clean diagnostic reports.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49822 b2dd03c8-39d4-4d8f-98ff-823fe69b080e