In my Cabal file I have defined a flag that controls whether tests are
built or not.  Now I'd like to hook it up a bit more so that './Setup.hs
test' actually runs the tests.

I haven't found a way to access that configuration flag in my hook
though.  Is it not available in some way?

Currently I'm settling for calling 'withExeLBI' and triggering the
running based on the exe name.  That feels somewhat circuitous though.
Is there some better approach?