weakref behavior

gistfile1.txt

This is from the end of weakref.rb:

if __FILE__ == $0
#  require 'thread'
  foo = Object.new
  p foo.to_s                    # original's class
  foo = WeakRef.new(foo)
  p foo.to_s                    # should be same class
  ObjectSpace.garbage_collect
  ObjectSpace.garbage_collect
  p foo.to_s                    # should raise exception (recycled)
end

And this is the output from running it (no exception raised):

"#<Object:0x000001010b3ea0>"
"#<Object:0x000001010b3ea0>"
"#<Object:0x000001010b3ea0>"

Any thoughts on why? I haven't yet delved deeply into the code.