I'm still to be, and don't expect to be, convinced of the value of \t directory and Test:* modules.

Don't misread that. I'm strong on tests and testing. It is the only tool short of suck-it-and-see that we yet have for trying to establish the quality of the code we produce.

The problem with those modules and the \t directory is that they rely on tests external to the code. Out of site, out of mind. Tests should be integral with the code where they may be maintained along with the code. You can have all the tests in the world but if they are testing the wrong things they are little more than overhead.

In an ideal world, the tests would be generated automatically by the compiler thereby removing the possibility of the tests and the code becoming out of sync, but that is still a ways off.

Design by contract shows great potential (IMO). I had hoped that something similar would be integral to P6, but I haven't seen any signs of it. I'm hoping that the (proper) macro facility will allow this to be added in fairly short shrift after the fact. Time will tell.