Matt Miller wrote:

... depending on the type of process you're dealing with, it may not be physically possible to test every single permutation, so - yes in some cases you might not be able to completely dummy-proof or fail-proof some jobs.

Maybe not, but it's no excuse to bypass developing the appropriate test cases, either.

The time spent actually writing software should be almost vanishingly small, compared to the time expended on design up front and testing in back.