In this case I think it's okay to just change the existing test to work with Throwable rather than add this new one.
I don't see any value in having them both since an Exception is a Throwable.  If we still wanted to test both Exception and Throwable then we could also just wrap the existing test in a doseq like:
`(doseq [[error message] [[(RuntimeException. "oops") #"java.lang.RuntimeException] [(Throwable. "oops") #"java.lang.Throwable: oops"]]`