> If the API is more like self.assert*()'s "msg" parameter which appends 
> data to the usual exception, then it will be the same as what people
> are already used to.

It might be a good idea to allow both this and the arbitrary parameter kwargs, then.

> I'm not advocating independent addressability/runnability of subtests
> or the following approach, but a naive way to do this would be to run
> the TestCase as usual, but skip over any subTest blocks if the
> parameter data isn't an exact match.

Well, I still don't know how to skip a `with` block (short of raising an exception that will terminate the entire test).