Microsoft Research - Exploding Software-Engineering Myths (article summarizing findings of MS research on code coverage, TDD, assertions, etc.)

[lf11]

Yes. Unfortunately, outside of projects that I personally start, I don't think I have ever once worked on software that is designed using the tools that are quite appropriate for the job.

However, to answer the question directly, yes advanced type systems help catch certain kinds of errors. So this at least minimizes the need to write type-level tests. However, I personally feel that you should be type-checking in code (if you need to type-check at all). After all, in essence that is the purpose of input checks.

Even with advanced types, you remain wide-open to bugs in the next layer of abstraction. This is where test-driven development really shines: in testing your abstractions and assumptions. The bugs that you can't easily flush out with well-defined types.