this should fail

hi David, when playing with the changes in the last pull request i found this weird behaviour: i was trying to check whether my understanding of `wrap` was correct, thus i wrote a doctest, but i was too lazy so i tried to run the tests to see the result and eventually paste it into the doctest. Anyhow, contrarily to what i expected, the tests do not fail. What am i missing? I am doing the pull request not for merging obviously, but just in order to show the problem