ruby2gv doesnt recognize script

[Alejo Izquierdo]

Hi:
I just installed gem and graphviz by apt-get. All examples work ok, but ruby2gv's doesnt.
i am trying to convert a ruby script but it only makes a png with script's name inside. I tried some forms but all is the same.
I was looking for docs about ruby2gv but the example is unavailable and I dont see any more in github.

I type :
ruby2gv -Tpng -ocheck.png test.rb or "test.rb"

and I receive file adjunt check.png

Could you tell what I'm doing wrong?
Thanks

P.D.: thanks for your great work