Talys said:bwud said:... regression test to ensure nothing went wrong with the rest of the code - which it will so then you'll have to trouble shoot and repeat until regression testing passes.
People who aren't in the product/software development industry don't consider regression testing =X
As you add stuff, you need to make sure it doesn't break stuff that's already there and working, and as a product becomes more complex, this becomes more and more time consuming and complicated, both to test and fix.
And if you're an honorable company, you also have to support your product by developing correct, well-written documentation, and by training your human support staff. Every feature adds incrementally to the cost of the device, as does every support call for a poorly-implemented or poorly-documented feature.