> Unit testing ... are only available at the higher price levels.

Actually, this is now available for everyone, something I advocated for. VerificationTest and TestReport are the key functions there.

Good implicit suggestion about QuickCheck.

We've supported unit testing in our Eclipse plugin for years, and with V10 brought the MUnit package into the System context with a redesign of the essential functions.

Yeah quickcheck (and smart check which minimizes the counterexamples) seem like places where mathematica could shine bright for software debs.

I would absolutely adore seeing smart check implemented in Mathematica. Please make it so.

There's the beginnings of an algebraic type system hiding in 10 (do Get["TypeSystem`"], then try RandomData[Vector[Atom[Integer]]). So generating synthetic data for a function with a given signature is already possible. Now we need to be able to express invariants etc, and then minimize counterexamples.