Check y

By using the get_debug_values() function and with flag "theano.config.compute_test_value" turned on, we can now check the value of Y before computing kl or elemwise_kl. Note that this feature should only be expected to work in test time, not for passed values in a real function call.

Should we check every mode of "theano.config.compute_test_value" in the unit test? Or, since it is only a unit test for kl (or elemwise_kl), just testing it on one of the mode will be OK?
The behavior I want here is:

    If kl() normally returns with a wrong Y input value, then raise an Error flagging that kl() does not past the test. 

So, which kind of Error do you think is proper for this situation? And will that be considered an error by nosetests if I print sth to stderr?