I'm not exactly sure when it happened, but it appears to be the case that the avoiding_non_differentiable_code test suite is printing an awful lot to the terminal. It would be great if this could be suppressed somehow. I had to do this inside the standard testing functionality (see the test_rule function in #389 -- for some reason I can't link to it directly) to make doctests work sensibly, so I wonder if similar bits of Julia functionality can be used to sort this problem out.