fails:Signal.trap ignores the signal when passed nil
fails(JRUBY-5666):Signal.trap the special EXIT signal code runs the proc before at_exit handlers
fails:Signal.trap is possible to create a new Thread when the handler runs
fails:Signal.trap returns SYSTEM_DEFAULT if passed DEFAULT and no handler was ever set
fails:Signal.trap raises ArgumentError or Errno::EINVAL for SIGKILL
fails:Signal.trap raises ArgumentError or Errno::EINVAL for SIGSTOP
fails:Signal.trap accepts 'SYSTEM_DEFAULT' and uses the OS handler for SIGPIPE
fails:Signal.trap allows to register a handler for all known signals, except reserved signals for which it raises ArgumentError
fails:Signal.trap raises ArgumentError when passed unknown signal
fails:Signal.trap calls #to_str on an object to convert to a String
