I'd like there to be a cleaner conceptual break from 'testing' and contracts. I could understand the contracts being incorporated into testing but I don't mentally file them that way and it'd be a shame to have a general purpose module that acts on functions with unrelated bits stuck in.

The overall idea, I like. Contract::File::Test might have your testing-specific code in it. My assumption is that in using this sort of thing that the module user would be using things like Params::Validate and throwing exceptions somehow. Maybe Exception::Class as well. Or how to signal contract failure?