As Dijkstra used to say, “Program testing can be used to show the presence of bugs, but never to show their absence.” In other words, while we may find more bugs by simply testing more, our test suites, however large they may be, will never ensure that the software system is 100% bug-free. They will only ensure that the cases we test for behave as expected.
This is an important principle to understand, as it will help you set your (and your customers’) expectations. Bugs will still happen, but (hopefully) the money you pay for testing and prevention will pay off by allowing only the less impactful bugs to go through. “You cannot test everything” is something we must accept.
NOTE Although monitoring is not a major topic. I recommend investing in monitoring systems. Bugs will happen, and you need to be sure you find them the second they manifest in production.
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