One thought that might be nice is to persist the output results into a Prolog file (thinking library(persistency)) so that the results can be loaded and queried directly. This would be in addition to a formal format as proposed.
The nice think about having a persisted Prolog file is that it could include info that is not part of a standard format which can also be queried with Prolog.
If I understand the proposal correctly then one of the side benefits of a standard output format would be the ability to use a third party GUI that understands the format to control the running of the tests. Note: Image only to get an idea of what such a GUI interface would look like, not as a recommendation for the particular unit framework.
(Image from Wikipedia CsUnit)
The only other unit testing framework I have had extensive experience with in the past is xUnit.net which derived from xUnit. I used it often when developing F# code and it made running test enjoyable, writing test were still a pain. A side benefit of the GUI was also seeing code coverage and grouping test into categories (think labels) such as new tests for a release, bug, enhancement, … .