I definitely agree with the statement about prototyping and testing. Testing is another signal of quality, a guarantee if you will, to your stakeholders that your software provided is dependable and trustworthy. That doesn't matter if you have no customers to begin with!

I'd also like to throw it out there that testing can be especially helpful when writing code against known problems. Some benefits are:

- Since you already know the problem domain, your test writing will be extremely quick and effortless, so the benefit of having that test in the first place far outweighs the time/effort invested in writing them.

- In dynamic languages especially, typos are what kills you in this situation. Testing will quickly catch 'em as you program.

- Finally, testing will force you to think more about the edge cases, since implementation is a straight-forward process. Thus, you'll spend less time later doing QA and have an overall more polished feature.