Testing by itself does not improve software quality. Test results are an indicator of quality, but in and of themselves they don’t improve it. Trying to improve software quality by increasing the amount of testing is like trying to lose weight by weighing yourself more often. What you eat before you step on the scale determines how much you will weigh, and the software-development techniques determine how many errors testing will find. If you want to lose weight, don’t buy a new scale, change your diet. If you want to improve you software, don’t just test more; develop better.

-Steve McConnell