Yeah, I figured out it was loader only errors after I read the code :)

"load_tests not called" is very different from "load_tests produced an exception", so the text of the error message should be changed accordingly.

I understood your use case more-or-less, my question was, why is the error *string* the thing returned?  Given that the synthetic test encapsulates and re-raises the error, might it be more useful to store the exception object in the errors attribute rather than the message strings?  That would seem to provide more introspectability.