There is a quote from one of Richard P. Feynman's books where he talks about his involvement in the Challenger disaster inquiry. He was very impressed with the rigour that the software team applied to testing the flight control software. They used the quite sensible method of building the code up from small and testable components, right up to the full simulation.

Apparently a manager from NASA had wanted to try to save money by cutting back on the testing and had said to the team. "Why bother with so many tests? You always pass them anyway!".